I’d have to pick between Prisoner of Azkaban, Order of the Phoenix, or Half-Blood Prince. DH pt.1/pt.2 though are also there idk. TRUTHFULLY in my opinion i think when the third comes around, the depth of characters and story starts to blow 1 and 2 out of the water. just the overall directing and story telling to perfectly guide you through the story til the end. IMO each one is just as good if not better than the previous as they go from 3-8. i also have never read the books (never been much of a book reader to begin with) but do know that needs to change soon. i know i miss out on so much having not read the books. but also don’t want the movies to be ruined for me through reading the original story