I am going to ignore the complaints that the movies did not necessary stay faithful to the books and a lot of things were cropped out.
However, imagine if you are became a fan of the series without reading the books, only watching the films. what will be the best harry potter film just from a quality and film making point of view? Let's try and be objective not subjective since subjectivism may be too influenced by your individual favourite.
I have allowed multiple choice since I believed it is tied between 3 movies.