Hard Choice! I love Robert's portrayal of Durza in the film; however, I feel that he is given more depth in the book.
Though, now that I think about it, that may have been because it wasn't limited by time like the film was...
Gar! How about both?

His character is a lot deeper in the book but I really liked his portrayal in the movie. He seemed to be the only character they did a good job on. The only thing I hated were those random cut-scenes between him and either; the Urgals, Ra'zac or Galbatorix. Those are not necessary.