I'd say the Heat. Even tho the C's have taken care of the 76ers Joel Embiid still scares me at least a little bit. If he can get his groove back he COULD be the best player in a playoff series against the C's and make the series close.
I know the Heat have played the c's tough, but unless they out-shoot the c's 43% to 30% from three like last year I just don't see how they win a series, or even make it close. Plus I'd very much like the chance for the C's to just crush them, I think it would be over in no more than 5. But maybe that's hubris.
Bottom line: If the c's are as good as we think they handle these teams and get to the Finals.