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Between the two, I like Keaton more, even though I prefer Batman Begins and The Dark Knight over Batman (1989) and Batman Returns (I consider The Dark Knight Rises to be as good as Returns).
The thing is, you can see someone like Christian Bale be Batman. He has the muscles and the money - you can see him pummeling the underworld of Gotham with his fists and toys. He's an awesome Batman, looking menacing and fighting ferociously (a better martial artist Batman than Keaton's, honestly), but I think he slightly lacks in the Bruce Wayne department (still did awesome, though, no gripes here).
Keaton, on the other hand, plays both sides well. As Bruce Wayne, he looks like he wouldn't fair well in a fistfight, which is perfect as it helps with him trying to not let people know he's Batman (outside of the few he told), whereas with Batman, he may fight with the ferocity of Bale's Batman, but he gets some damn good hits in there. Also, he can pull off being terrifying as well.
Overall, I find that Keaton just slightly edges over Bale, though they are my top two in live-action Batman portrayals. In comparison, I think West, Kilmer, and Affleck all have their pros and cons that equalize the other, and Clooney...well, he's a good Bruce Wayne, or would be with the right script.
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