It's been thirty years since Batman '89.
Michael Keaton: a good Batman, a very credible Bruce Wayne with an eccentricity that really worked well. Michael with his style could pull off that psycho quality even without the Batsuit that gives the entire performance an edge.
Val Kilmer: an okay Batman, a credible Bruce Wayne. His Bruce was pretty staid and I don't recall his Batman having any iconic moments like Michael, but overall, he was decent.
Christian Bale: a good Batman. Given how well Nolan used Batman in the shadows, it did hurt Bale as Batman as he really didn't have a moment, though the one at the end with him and Gordon on the roof was probably the best Batman and Gordon moment in the modern era. His Bruce was excellent as far as the party animal type.
Ben Affleck: haven't seen him.
Those two guys in the running I don't see as working. They'd better be willing to put in the time in the gym to bulk up if they think they're going to pull off Batman.