The Dark Knight: deeper meaning, slightly more emotion, more powerful imo
The Dark Knight Rises: more beautiful ending, brings things full circle... the ending with Blake was awesome, but some part of me wishes that it ended with Bruce Wayne in the final scene before the credits, since the film is called The Dark Knight Rises... but that's just me (since all 3 films ended with a shot of Batman/Bruce Wayne)
either way, both endings are VERY close for me, they both have the same music, the same type of montage showing where the characters go from there.
The Dark Knight wins by a hair.