Everyone was pretty great, but I'll go with Bale.
Even with such an ensemble cast, obviously the movie rested on his shoulders. Make no mistake, this movie belonged to Bruce/Bats, not to the villains. Bale was probably in 95% of the scenes.
Like Christopher Reeve made you believe a man could fly, Bale made you believe a man could dress up as a bat to fight crime. He was believable. He was driven, without coming off as psychotic.