I really liked Prisoner of Azkaban. It was pretty close to the books (as were the first 2 but PoA had a big tone shift). The whole feel to this movie was great, and I liked getting introduced to Remus and Sirius. The one thing I didn't like about this film is how they cut out the whole Marauder story line which could've been really quickly explained.

I also really liked Goblet of Fire, despite many changes.