Bale Batman is GOOFY. Grating voice, ugly suit, a characterization that takes a nose dive in the third movie, etc. His best performance is in the first movie and mostly when he's out of costume. His Batman acts like he got hit in the head with a ****ing baseball bat and his mouth is always open like he can't breathe.
Affleck Batman is a big oaf. He's in two awful movies, and seems stiff and uncomfortable. There's nothing graceful about him. His electronic voice, while not as bad as Bale's Cookie Monster voice, is still strange and awkward sounding. He's like a cave man. The more you see of him, the worse he seems to gets.
Both have their moments though. Bale is cool in Begins with the Flass interrogation scene and Affleck has (well had) a cool costume and things like the warehouse scene.
tl;dr
They both suck. Makes for some cool action figures and dolls tho.