Considering Ana Steele, in many ways, is just a tweaked, R-rated version of Bella Swan, who is bland and boring herself, I would say Ana. Christine, while Emmy Rossum's take is probably not the best, is still far more interesting than Ana.

Lame and uninteresting character, matured version of Bella Swan like the others said. Have no idea who is Christine.

By far

Anastasia isn't even a character. Christine had at least some essence of development if only an essence of it.

Emmy Rossum takes a bland and boring character and makes her even more bland and boring (add emotionless to the mix), but Anastasia is barely even a character.