I never thought Katie Holmes was particularly pretty. She is attractive, but every time she talked her face became slanted or something. It was very strange and distracting for me. Maggie isn't as attractive as Katie but I think she is a far superior actress so I was happy when she was cast and liked her in the role more than Holmes.
Katie is attractive but she has too much of a Dawson's perky quality to seem like she fits in a world like Nolan's Batman. Maggie has a greater rang of emotions she can convey and meet te needs of the moment an fit in very well for TDKR.