HULK. I have been a Hulk fan since I was a kid. Smash, smash, and smash some more. Nothing else need be said.
I always thought Thor was kind of goofy. His standalone movie improved my opinion considerably.
I never cared one way or another about Iron Man until his first movie kicked so much ass it wrapped around the universe and started kicking itself from behind. Now I like him.
As for Cap, Widow, and Hawkeye -- eh. I like for my heroes to have powers, something to set them apart (aside from years of training, of course). Just a personal preference. Avengers did as good a job with them as everyone else, I was as interested in them as I could be.