Well, I must admit that I have never seen Spirits Within. However, from what I've heard about it, it is very much like Advent Children in the fact that it's a cult film. However, it would seem to me that AC would be a better cult film because of the fact that the game provides the backstory, while with SW no such thing exists to provide that kind of information. Overall though, most people have had a much better reaction to AC then to SW, so with my limited amount of info, I'm going to go with AC being better.