Right now, I would prefer to play the Cavaliers since Orlando has been much hotter as of late. Cleveland has to integrate a lot of new players, though, and they may become a better team by playoff time.
Any team with a LeBron on it is dangerous- you can't afford to have Cleveland close at the end, but they are beatable. Orlando can score a lot of points and shoot from the outside and they are playing their best ball right now. Philly has shown they can finally play with Orlando, but I'd like them to win against another playoff opponent first to build up their confidence.
Out of the top 4 in the East, I think Cleveland is the most vulnerable, then Orlando, then Detroit and finally Boston.
The Sixers can't get to the finals unless Boston falls, and I don't think that will happen. But if the Sixers can get to meet Boston in the playoffs in the E.C. finals or semis, that would be a real accomplishment.