I'm a little surprised that Keaton's lead is so great, but I certainly would pick him as my favorite non-animated Batman to date. He had a remoteness and quirkiness that both humanized him and showed the damaged psyche of the character.
His depiction is also helped by some great (art) direction. There's plenty of shots of him just brooding in large rooms of his big empty manor. I've always loved the shot of him sitting in his dark library with the bat signal lighting up the room. It is iconic, and I think the dark blue overtones really fit his character well. And then of course that fantastic Elfman score comes up... ah, gives me the chills. To think that they took the extra effort to explain how the bat signal makes its way through the window, via automated mirrors outside his manor. They didn't have to explain it, but they did.
Bale was fine, but a little bland coming from the actor that had such a bravura performance in American Psycho.
Yeah, I never felt like he made the persona entirely his own. He's just Bale being Bale. Servicable, but he did not embody the character entirely.