A lot of people agree that there's no more definitive version of Batman than the animated series.
When it comes to animation or comics, I always think in Kevin Conroy's voice.
I admit though, out of all the live-action Batman portrayals, I think each performer had something missing from the other. For me, Michael Keaton will always be Batman. Some may argue that Val Kilmer portrayed the best version of Bruce Wayne in terms of his serious personality, but for me, he lacked Bruce Wayne's cranky side. Keaton and Conroy did it for me. Kilmer didn't seem to have the playboy personality down though. He acted too casual in public. As for the look of Batman though, I thought Kilmer did alright, and he was fairly intimidating. He almost sounded like Conroy's Batman.
Still, all of the other Batman portrayals, excluding Keaton, seemed to be missing something one way or another. Say what you want about George Clooney, he often plays the same characters, but in other movies I've watched him in, I realize, wow, he actually could have been the perfect Bruce Wayne, if only he had a better script and direction. He got the playboy persona right, but aside from that, he wasn't believable at all as Batman or Wayne, and was pretty much a joke.
As for Christian Bale, the actor has stated repeatedly over time, that he never had a real interest in the character. I think he tried too hard with his performance at times. Bale's Batman voice took me out of the character. His Bruce Wayne mask was over-the-top to me, but had his moments. I could see the sadness in the character, but didn't really see his cranky side. Compare the 1989 Batmobile chase scene to Batman Begins' Batmobile chase sequence, the way Bale talks to Rachel in that very, soft and almost loving kind of voice, whereas Keaton's Batman coldly ignores Kim Basinger's character throughout the whole drive. I just thought this was one of the main reasons, apart from fighting crime, that made him a badass.
Ultimately, I think Michael Keaton got the personality of Bruce Wayne down perfectly. I think maybe his eye brows gave him an advantage. The look in his eyes. He had the Batglare. Bale looked too boyish. I am aware of course that they got a lot wrong in Tim Burton's version of the character, making Batman a cold-blooded killer (well, to some extent). I was never able to see Bale's Batman as cooler.
Ben Affleck comes as a close second favorite Batman to me. I think he got the Bruce Wayne part down perfectly, however, as Batman, I think he's good, but every time he speaks with the robot voice, I always miss Kevin Conroy's voice. Because it is a voice modulator and not his own. At least it's not Bale's voice though. So I can never fully see him as Batman, but almost. Aside from the actor's contribution, I think the music also contributes to a certain degree.
Whether it was Keaton though, or Conroy, their voices, their delivery was so profound.