I have to admit, aside from all the massive failures on the part of the writers and director, I think Val Kilmer was the best Batman so far as well. This has much to do with the fact that both the Batman and Bruce Wayne had more screen time and character development than in the first two movies. Overall, the first two movies are the best, but Batman got screwed both times as a star. Michael Keaton did a great job with what he was given, but it wouldn't be hard to surpass his performance if the writers allowed Batman to shine.
I think Val Kilmer's a punk, but because Keaton was barely allowed to talk, and George Clooney (who I do like a lot) is just not right for the current incarnation of Batman, he did a pretty decent job with what he was given. It would have been much better if he had been told to do and say the same kinds of things that Keaton did. Of course, there was too much wrong with that movie to salvage it, really.
Clooney got a lot of shit for his part in Batman and Robin, and he admitted he killed the franchise. This is not true. If anything, his Batman got the least character exposition, and he was probably told by the director "Be yourself, George. That'll be a lot more family-oriented than if you act like the Batman."