If we’re being honest with ourselves, there’s only one correct answer - ourselves. Barring injuries, there’s just no one in the East that should theoretically beat us in a 7 game series on a talent basis. That said, our over-reliance on the three leading to huge variability, tendency to crap the bed in crunch time scenarios, questionable late-game coaching decisions, etc. all have plagued us at various points the last few years.
As for other teams, I still think it’s narrowly the Bucks, at least in terms of potential. Though it’s questionable whether they’ll ever get there, especially this year with the coaching change.
For the Sixers, I just don’t trust them in the playoffs given their history, as well as Embiid’s foul-baiting gameplan not translating to postseason play.
You can also throw the Heat in there as a consideration post-Rozier trade, but I’d have to see how they play with him first before putting them there.