Michael Keaton. He's the only one who I think convincingly portrayed both Batman and Bruce Wayne. He's the only one who managed to play Bruce as charming and debonair, but also with a slightly unsettling, unpredictable element.
Bale's Batman was menacing (though the gravelly voice got so absurd it became a parody of itself), but his Bruce was too cold. Though I don't think Bale can do warmth anyway. The last time I found him charming or sympathetic in any way was in Empire of the Sun.
The less said about Kilmer and Clooney, the better. And I never liked the Adam West Batman, even when I was a kid.