Even without Middleton, I think the answer is still Milwaukee. Giannis is just an absolute monster. Hardest guy to defend in the sport. Can go to coast to coast, blow by you on the perimeter, back you down, or just post you up. So long, strong, and fast. Even without Middleton, I just don't like what Giannis can bring when you are trying to guard him. Wouldn't be surprised to see a 40 spot every game in the series (especially if Middleton can't go and he needs to do more). And it is hard to overcome that sort of game from your opponent when it happens every game in a 7 game series. And it isn't like it was just the Giannis and Middleton show in Milwaukee, Holiday is an excellent player, and their role players i.e. Lopez, Portis, Allen Connaughton, Matthews all know what they are doing. The Bucks are just a well constructed team around the best player in the world.
Miami is very good, but I just don't think Butler can do it every single game over a 7 game series and they need Butler to do that for them to really compete for a title. I remember in the Finals 2 years ago, Butler had 2 massive games, and 4 ok games. Not unsurprisingly, the Heat won the 2 games where Butler really showed up and lost the other 4. I just don't think Butler is in the same class of player as Giannis, and that matters a lot.
Embiid certainly has the potential to be a Giannis level impact, but I don't trust his health or his supporting cast. I'd be pretty darn surprised, maybe even shocked, if Boston lost to Philly. I think Embiid would have to go for something like 40/15 every game for that to happen and I don't think Embiid can string 4 in 7 like that with his frailty (especially since it would after another full round on that thumb).