INTRO:

Standard Bant MidRamp list. 
Our general gameplan is something like this:

• Early game (turns 1-3): treading water. We play Growth Spiral and Uro, Titan of Nature's Wrath to accelerate into our nasty threats at 5 and 6 cmc. We also have options like Teferi, Time Raveler to slow down Aggro decks or set ourselves up for success against Control decks.
• Mid game (turns 4-6): pivoting. We start playing some of the best cards in Standard a turn ahead of schedule. For example, we land a turn 4 Nissa, Who Shakes the World and, if we get to untap, they probably lose because it only gets better from there. We also have removal to work around dangerous board states. If they go wide, we go Shatter the Sky. If they go tall, we go Elspeth Conquers Death. Once the board is under control, we turn the corner and let Hydroid Krasis, Dream Trawler, or Uro, Titan of Nature's Wrath dominate. It's the beginning of the end. 
• Late game (turns 7+): going over the top. We go straight over 99% of the format by chaining massive Hydroid Krasis, which restocks our hand and heals us regardless of removal or denial. If removal is an issue, Dream Trawler steps up with its hexproof. If denial is an issue, Uro, Titan of Nature's Wrath steps up with its recursion via escape. This deck has angles for days.

I encourage folks to break the deck down to its core/shell and tweak it from there. 
Here is what I would use as a shell for the deck:

4x Uro, Titan of Nature's Wrath
2x Hydroid Krasis
2x Dream Trawler

4x Growth Spiral
3x Elspeth Conquers Death
2x Shatter the Sky

4x Teferi, Time Raveler
2x Nissa, Who Shakes the World
2x Tamiyo, Collector of Tales

+Lands (28-29)

Add and subtract cards from there to your liking.

I made a maybeboard of cards that are worth thinking about. Some I dislike but others swear by (e.g., Arboreal Grazer), some I'm currently/considering testing (e.g., Hushbringer), and others are ideas for future reference (e.g., Neutralize). Check it out if you need some inspiration!

SIDEBOARD:

The sideboard is highly customizable and will depend on a combination of your main deck choices and, more importantly, the meta. That being said, here is the half of the sideboard that I wouldn't recommend touching unless you're confident (I often struggle with sideboards so you'd be in good company):

3x Devout Decree
3x Aether Gust
3x Mystical Dispute

Tweak the other half to your heart's content. In fact, I encourage it. This is a phenomenal deck to grow your sideboard construction skills. Bant has access to some of the most powerful cards in standard (and imo the best sideboard options). Flex those muscles. It was a proud moment for me when I thought of putting 1-2 copies of Questing Beast in the sideboard and the following week saw a couple pros doing the same.

I'm very confident in the 3rd Mystical Dispute and 3rd Devout Decree. I'm also confident in having at least 1 Agent of Treachery for control mirrors (this card also instantly wins you the game if you resolve it against U/W Blink and steal their Thassa, Deep-Dwelling). I think Heliod's Intervention is a very versatile card, but its fit depends on the current meta. A 3rd Aether Gust is very reasonable (you could even main deck the 3rd copy).
The last few slots are in flux. If you find yourself struggling with a particular matchup due to deck construction (i.e., not player error), think about those last few slots. For example, you could try Hushbringer for its sideboard value versus decks that rely on Cat/Oven or Blink effects, and its synergy with Uro, Titan of Nature's Wrath. 

ADVICE:

Get comfortable tweaking the deck. Start with small decisions and progress to bigger ones (e.g., do I run any Narset, Parter of Veils?). My best advice is being thoughtful and thorough about each decision--have a reason for every copy of every card you include. Again, Bant has access to some of the best cards in standard, so every slot in this 75 matters. A lot. 

Game 1 can be a struggle for this deck in several matchups, especially Aggro decks like Mono Red and Rakdos Sacrifice. These decks can (and often will) run you over in game 1, but the matchup feels very reasonable post-board. I recommend including a couple main board tricks to give you a shot in game 1, but do not go overboard--you risk throwing the matches you should be winning. For example, we can main board a 3rd Shatter the Sky. Not drawing your sweeper against Aggro can be a death sentence, so one extra copy of this make-or-break card is a small price to pay (and it's not terrible in most matchups imo).

One of the most common mistakes I see with Bant MidRamp is people keeping bad hands. Practicing your mulligans with a simulator could be useful. Here are the top 3 things to keep in mind:

• It's hard to flood with this deck. You have 8-10 scrylands fixing your draws, and the type of ramp we use is useless without extra lands. We run 28-30 lands for a reason; don't be afraid to see 5 of them in your opening hand (especially if a couple can scry)!
• Missing land drops 4-5 can be game over. I am always happier to see 5 lands than only 2 in my opening hands. Having 2 lands plus an Uro/Spiral is rough; having 5 lands plus an Uro/Spiral is smooth sailing.
• Your top end is designed to reward you for investing in your mana base. Nearly half of your payoffs involve cantrips or straight up card advantage. We run the full set of Hydroid Krasis (aka The Notorious JHB) for a reason; he and Dream Trawler (aka Birdman) appreciate seeing 6 lands in quick succession. 

Play testing results:

Arboreal Grazer: I tried 2 copies for a few days and did not like it. Others swear by this guy, but I would not recommend more than 1-2. It's just not the kind of ramp we're (most) interested in at such a steep cost in card value. There's a fair argument for him as an anti-Aggro tech, but I think we have better tools.
Edit: There's another argument for this card that I should have mentioned more explicitly before. That is its "high roll" value. I can't deny that turn 2 Teferi, Time Raveler and turn 3 Nissa, Who Shakes the World are powerful. I may test 1-2 copies of this guy again one day--I admittedly did not test him as thoroughly as I tested Tamiyo.

Tamiyo, Collector of Tales: I tested the deck with 0 and 2 Tamiyo. Drawing both copies of Tamiyo felt bad sometimes (primarily versus Aggro), but it's highly unlikely in shorter matches. It's important to note that the long, grindy games in which you're more likely to draw both copies are the games in which she's at her strongest. I've heard at least one pro refer to her as a "do nothing" card (not naming names because that's not the point) for Bant Midramp. I think this is an understandable evaluation of the card for someone whose experience with the deck is, in all likelihood, one day of playing it on MTGA. I mean that sincerely and with no disrespect. Be careful of these evaluations from people, including pros, whose experience with the deck is so constrained. It's not that they made a bad call; it's that they didn't have enough time or data to make a different one. For example, Aggro could have simply been popular that day--I kid you not, this happens all the time (on MTGA especially). If you're unsure about this choice, running 1 copy is safe. In sum, Tamiyo occupies a unique space on the mana curve for this deck, has great synergy with Uro, Titan of Nature's Wrath and Elspeth Conquers Death, and has high enough loyalty to offset this deck's inability to protect her early in most games. She's worth at least 1 slot in the 75. See Update 3/25 for more related to Tamiyo's spot in the deck.

Update 3/25: Removed 1x Uro, Titan of Nature's Wrath (down from 4 to 3); Added 1x Omen of the Sea (up from 0 to 1). I had been looking for a way to fit a single Omen of the Sea into the deck for a week or so now. I think one copy of this card is smart. It's a welcome addition to the lower end of your mana curve, and there are times that you want to minus Teferi, Time Raveler for the card draw and not having a target feels bad. One copy of Omen of the Sea gives you a freebie target for the rest of the game. If I don't like the results, I may try 1x Arboreal Grazer in that slot.
If you don't want to trim any Uro, Titan of Nature's Wrath, you could look at trimming a copy of Tamiyo, Collector of Tales or Shatter the Sky instead. If Aggro is less prevalent in the meta, trimming the 3rd sweeper is the obvious choice. Trimming an Uro or Tamiyo is a bit awkward because they synergize so well together. After trimming an Uro, I'm considering also trimming a Tamiyo for a 29th land. The reason is simple: missing your 5th land drop (sometimes even 6th) is RIP.

Update 4/5: Minimal changes--mostly small tweaks adapting to the meta. This might be the final update before Ikoria, but we'll see if there are any major shakeups. I plan to update the list for Ikoria--there's currently no reason to believe this archetype will be less viable in Ikoria. Anyway, here are a few points I thought worth mentioning:

• I think main deck Aether Gust is correct. Having 2 copies in the main deck goes a long way. It's bad in very few matchups and, even then, it's never a 'dead' card because you can use it to bounce a Hydroid Krasis, etc. 
• If Temur Adventure has become less popular in your environment, feel free to drop the 1x Heliod's Intervention in the side board.
• Make sure you're running a lot of Devout Decree and Aether Gust; seeing 4 of each card in a list of 75 is not overkill. You can main deck some Gusts (I like 2), but do not main deck Decree. I know this is obvious to many folks, but I want my write ups to be accessible to as many people as possible.

Update 4/11: Final update before Ikoria! I haven't made any big changes to the list, but I wanted to quickly comment on a couple important trends we've seen over the past week re: the latest popular iteration of Bant MidRamp and its success.

• The latest (and currently most popular/successful) Bant MidRamp list trimmed Nissa, Who Shakes the World and Hydroid Krasis to 2 of each. I like this iteration a lot, and I trimmed to 3 of each in my own version that I've been testing. This gives us room for main deck copies of Mystical Dispute and/or Aether Gust, both of which are safe and powerful inclusions in the final days of TherosBD meta. It feels solid.
• Many Bant MidRamp lists have completely abandoned artifact/enchantment removal (most notably Knight of Autumn). I'm surprised to say I don't dislike this move. It's worth noting that these lists tend to run a 4th Elspeth Conquers Death and I don't think that's a coincidence. The most problematic artifacts/enchantments in the current meta can be removed with ECD (e.g., Wilderness Reclamation, Fires of Invention) for a much stronger play. This is partially due to the decline of Temur Adventures and thus the lack of Lucky Clover.
• There are a couple other minor things that are interesting but don't warrant more text here. I recommend checking the list out for yourself to see what you do/don't like. It's easy to spot from any recent online results.

***IKORIA***

Welcome to Ikoria! I'll begin my updates for this deck in IKO meta here. Bant MidRamp remains my favorite tournament deck for the moment and it's hard to imagine the meta evolving in a way that pushes us out. Let's dive right in!

What did IKO give us?

• Bad news: IKO gave us virtually nothing.
• Good news: we didn't need anything! 

That's right--our job as Bant MidRamp in IKO is less about figuring the deck out and more about adapting to the new meta. 

I have 3 plans/goals for this deck in early IKO:

• Tech more anti-Aggro tools. Aggressive decks are more popular when a new set drops. Plan to see lots of mono red, etc. Heck, I've seen more Rakdos Knights in the past 24 hours than I did the whole final week of THB meta. I like a 3rd Shatter the Sky main deck for this reason. Also, if anyone tries to get too cute with Mutate, you get to blow over their house of cards. Fun police, sirens on. I think some main deck Aether Gust is still fair too, but I wouldn't go over 2 for now. Something like Glass Casket could be a better choice depending on what flavor of Aggro people are pushing. 
• Don't get too cute with techs. I know this seems odd given what I just said, but hear me out. Most people fall in one of two camps right now: folks experimenting with new decks (e.g., Temur trying to break Song of Creation), and folks punishing the experimenters (e.g., Embercleave reminding "go big" strategies that they're on a clock). We do a third thing where we use this knowledge to keep them both honest. We keep the new stuff honest by sticking to our tried and true powerhouses, and we keep the aggressive lot in check with the anti-Aggro tech I mentioned in the previous point. For example, I think we keep Narset, Parter of Veils in the sideboard for now, and I would leave most (if not all) copies of Mystical Dispute in the sideboard. Don't worry, I suspect they'll return to the main deck in a few weeks.
• Don't be afraid to experiment a bit. Just because we didn't get many new toys doesn't mean the deck can't evolve. Been itching to try a couple Arboreal Grazer or Gilded Goose? Go for it! Heck, sideboard some Gemrazer and mutate those 1-drops into some beasties! See what you can come up. The most important thing you can do right now is simply observe the new meta anyway. You might as well enjoy it!

Update 4/21:

• Deck Updates: Everyone trying to get cute with entry effects (Gyruda, Doom of Depths, Yorion, Sky Nomad, etc.) means Hushbringer could join the sideboard once again. I'm sure Uro, Titan of Nature's Wrath would enjoy that, but Grafdigger's Cage is much safer. Side note: I think main deck Mystical Dispute is safer than main deck Aether Gust at the moment, which leads me to the next point...
• Meta Updates: Blue was powerful in THB meta and it's poised to be even stronger in IKO meta. Main deck Mystical Dispute is a go. I have a full set of 4 in my 75 and I don't think anything less than 2 is defensible at the moment. Speaking of main deck hate cards, let's talk about Aether Gust for a second. The 3 things keeping me from main decking Aether Gust (and maybe not for long) are: (1) the growing number of Lurrus of the Dream-Den builds, and (2) the prevalence of Azorius builds (control and blink). That said, I think running 1-2 main deck Aether Gust is defensible; I just wouldn't play 3-4 main deck like it's still THB meta. Side note: I'm still confident in 3 main deck Shatter the Sky and I've considered a 4th in the sideboard. 

Update 4/27: There's a real chance that the 60-card version of Bant MidRamp is overall inferior to the 80-card Yorion, Sky Nomad version. I've played both and, while both are good decks, it's hard to say no to Yorion, Sky Nomad as a free card. We're trading one type of consistency (smaller deck, better chance of drawing any single card) for another (guaranteed Yorion). I will create a separate deck for the Yorion version. 

CONCLUSION:

Great meta deck right now with room to grow and adapt. Do not get too comfortable with any list of 75 for this deck--its ability to adapt is its greatest strength. Experiment with it and have fun!

A few thoughts on the overall deck as Theros meta comes to a close:

• White is back! Before TherosBD, White was in a bad spot. This deck has perhaps best showcased White's return to form with cards like Elspeth Conquers Death and Shatter the Sky. These cards are amazing by themselves and together. Shatter sweeps up early game threats and provides a panic reset for mid-late game if needed. ECD dominates the late game by simultaneously punching holes in their game plan while strategically boosting yours. We don't even have to mention Dream Trawler. White is no longer just the other many symbol you're forced to play if you want to cast Teferi, Time Raveler and that's fantastic. Let's be real though, you're still playing Teferi if you're in White. And why not? He synergizes perfectly with White's new toys. Instant speed Shatter? Recycling ECD? Yes and yes, please. I expect these 3-4 cards to remain one of the 'cores' of standard.
• Ramp has new options! Prior to TherosBD, Ramp in standard needed mana dorks (e.g., Paradise Druid). This deck takes a completely different approach thanks to Growth Spiral and Uro, Titan of Nature's Wrath. It's true we had Spiral before, but just 4 of these cards wasn't enough to power a deck. Having 7+ copies has opened new possibilities. We can ramp and use sweepers without worrying about losing our mana dorks. It's a big deal.
• Sideboards matter! I would not play this deck in Bo1. I believe this deck's matchups improve more than any standard deck in post board games. We can win matchups that we have no right winning. This is all thanks to powerful removal/hate (e.g., Devout Decree, Aether Gust) and good main deck tech (e.g., Knight of Autumn). This deck rewards the creative folks who push all 75 slots to the max. 

I hope folks have enjoyed--and continue to enjoy--this deck as much as I have. Thank you for reading and take care.