The reason Miami will most likely lose this is b/c OKC has too much offensive firepower for Miami, which simply lacks the offensive depth to hang with a team like OKC, esp. in 3pt shooting. These 2 teams play an eerily similar style, but OKC simply has better shooters. That will be the difference.
OKC is making 38% of its 3s in the playoffs, which is nearly as good as the Mavs did last year. Miami is shooting a pathetic 32%. That's the difference in the two teams' offense. If Miami had better 3pt shooting, I would pick Miami.
OKC has a smaller margin for error b/c their offense is so good.