I have the Thunder in 6.
Home court advantage will play a huge role. In order for the Heat to win, I think Bosh needs to have the series of his life. Ibaka and Perkins will make life much more difficult in the paint than Boston did, so they're going to need consistent play from Bosh to spread out the floor. Both James and Wade will need to be effective jump shooters in addition to taking whatever they can get in the paint. They also can't afford to have Chalmers and Battier vanish. These are probably the two best fast break teams in the league, so turnovers will be huge.
Unless Westbrook goes full on chuck mode, I just think the Thunder have too much.