I thought both Charlize and Uma did great jobs (probably the best of their careers), but i’d have to one up Uma just because I liked Kill Bill more and because I liked her more in that film than Charlize in Monster. Yes, Charlize gained alot of weight and had a great make-up job, but Uma lost alot of weight and physically toned her body for her role. But I think both of them performed to their max (and probably even more than that), and both showed a good deal of emotion and you could easily (well, maybe not as much in Charlize’s case) sympathize with each of them. But I think Uma did far more than just learn a different language and learn a couple of different martial-arts. I really felt for her character, maybe more so than any other character in any other film, and it was mostly due to her performance. QT’s direction defintely helped to define everything in the film, but there are some scenes that still give me chills down my spine, which were all due to Uma’s great acting ability. Take for instance the scene where Budd shoots her with the rock salt in V.2 and she spits the blood in his face. That look she has in her eyes alone is just about deserving of an Oscar imo. We as the audience also go through much more with Uma’s character than with Charlize’s in Monster. We see the awful things which led her to killing, but we can’t totally identify with her because she continues to kill even though we know its wrong. Now you may say that the Bride’s revenge in both Volumes of Kill Bill isn’t necessarily moral, but everything that takes place in the film is more or less fantasy and we can sympathize more easily with her because her enemies are seemingly more evil. Now alot of what i’ve been talking about deals with the direction and writing of both films, but I think that an actor/actress can only go so far with the material that they have. Uma Thurman as the Bride/Beatrix Kiddo had many memorable scenes in Kill Bill partly due to the great direction from QT and partly due to her just putting everything she had into the role. While Charlize Theron also gave it her all, some of her scenes didn’t have the same impact as the ones in Kill Bill because the script had a couple of mild flaws and the direction wasn’t as good as in Kill Bill, in my opinion.
So while I think they both perfected the roles they were given, I have to give the edge to Uma because I think that Kill Bill was a better film, which gave her more to work with, and I just really liked her performance better than Charlize’s.