Actually...I'd have to say Kilmer.
Simply for the fact that beneath the technicolor surface there was a VAST amount of potential.
Unlike West, Kilmer found the humor when necessary but could shift right into dark and brooding mode.
Unlike Keaton, Kilmer was able to pull off the public persona of Bruce Wayne the way it had been done in the comics.
Unlike Clooney, there was distinction between Kilmer's Wayne and Kilmer's Batman.
Unlike Bale, Kilmer's display of emotional torment and angst doesn't seem so displayed. You have to look beneath the surface to really get his portrayal in full. The psychology of Kilmer's Batman isn't as clear as Bales and is thusly a bit more sophisticated in its depiction regardless of the not-so-sophisticated film it was surrounded by. That and Kilmer's Batman voice, though no differintiation from Kilmer's actual voice, is just easier on the ears. I love Bale, but that voice has to go for TDK...probably won't though...
Give Kilmer and better director and screenplay...there could've really been something.
CFE