Spiderman 2 is either second or third with X-Men: First Class. Then I'd probably put the first Spiderman in fourth.
I honestly don't care much for the Avengers films.
When I first saw Captain America: TFA I loved it, but now I'm thinking I was just caught up in the hype because after watching it for the second and third time, it just doesn't hold up for me. I was never impressed with Thor. Ironman 2 outright sucked. The Incredible Hulk on the other hand I really enjoyed. People are always saying how terrible it is though and I haven't watched it in few years. Need to check it out again and see if it really is as bad as people claim. One thing I really liked about it was the tone. Thor/Cap: TFA/Avengers are just so cheesy and gaudy whereas I felt TIH was generally more dark, serious and dramatic. And lastly, the Avengers is a good movie, yet not nearly deserving of the praise it gets.
Ironman was just perfect though IMO.