Well lots of movies have several different genres...
Action: Can't remember something strictly action I enjoyed enough to call it best tbh. I'd say The Avengers but then I'd have three superhero films on this list..
Thriller: The Dark Knight (I put this here because, for me, though it's also a superhero film, its suspense and pace are its key attributes)
Romance: 500 Days of Summer
Comedy: Airplane
Horror: The Shining
Adventure: LOTR, Return of the King in particular
Fantasy: The Empire Strikes Back (you can switch this with the above depending on which you think fits better..)
Superhero: The Incredibles
Pretty mainstream list