...you can't do this to me!!! The Dark Knight is flawless, and Heath Ledger did amazing as Joker, but Avengers is so good...but none of those movies will compare to Dark Knight, but Avengers was so much better than any of the Iron Man's, Captain America, Thor, UGH I. DONT. KNOW.
The Avengers without a doubt. For me, it has everything a superhero should have: fantasy, action and humor. It was simply the greatest comic book adaptation ever made, because it feels fresh while being true to the tone of the comics. Simply amazing entertainment.