Six, absolutely.

I would have had Philosopher's Stone/Chamber of Secrets and the Deathly Hallows films share slots, so that the much more distinct Goblet of Fire and Half-Blood Prince could be on here. They're my three and two, with Prisoner of Azkaban being one.

Yeah, 6 is amazing for a single movie adaption. The earlier books have the advantage of being shorter books, so not as much to squeeze into that tight 150 minute window. I would have listed 1-6 for the poll. Hallows is a bit different because of the 2 movie split (sort of 'best adaption of half a book'...)

I like Goblet of Fire the most

Six

Six. The Half-Blood Prince was perfect.

In terms of faithfulness to the books, I'd say the first two; they feel almost perfectly transferred from page to screen. (And Chamber of Secrets, in particular is one of my favorites of the movies).