Michael Keaton, then Val Kilmer, then Christian Bale.
Batman Begins is my favorite comic book movie ever, with Ironman a close second. I haven't seen Dark Knight yet. Bale is a great actor (maybe the best on this list), but he didn't make Begins a great movie. A great script and the move toward the real tone of the comics did that. Keaton and Kilmer were better at being Bruce Wayne, IMO, and neither one used the annoying "Batman voice" when they were in costume.
George Clooney is also a great actor, but was a flaming turd of a Batman.
I never liked the Adam West Batman. I hate campy shows and movies, and West was the king of camp.