Empire Strikes Back. It had the best cues in my humble opinion, especially the snow battle and asteroid field.
I, personally, don't find the new Star Wars soundtracks to be that entertaining (in fact, I don't think I've listened to Attack of the Clones since I bought it). To tell you the truth, I much prefer Williams' older works to his new scores. The new ones are kind of screechy; quick bursts of high-pitched whistles too often. Of course, that's just one man's thoughts.