This thread is the promised follow-up to a thread that I made several days ago, asking what your favorite 'Harry Potter' novel is, which you can find here. As of May 12th, Goblet of Fire and Prisoner of Azkaban are both tied for first place, each with 24% of the vote. Chamber of Secrets is in last place with 3% of the vote.
Anyway, my favorite HP film is the Prisoner of Azkaban, it is just so odd compared to the others that I can't help but love it. My second favorite would be either Order of the Phoenix or Deathly Hallows - Part One.
I just want to add, that I think The Half-Blood Prince is ONLY good from a film-making standpoint, and that's it. It just diverted from the novel too damn much. It's a shame, since it's my favorite of the novels.