Most Helpful Guys
The one I enjoyed reading most was Goblet of Fire. It reminded me strongly of being that age. Deathly Hallows was satisfying, story-wise.
As for the films, the first was the most charming and the most like the book.
Book: Goblet of Fire
Movie: Prisoner of Azkaban or Deathly Hollows Part 2
Most Helpful Girl
Reading I enjoyed Sorcerer's Stone and Goblet of Fire the most, but in the movies I love Order of The Phoenix and Deathoy Hallows Part 2.