I'm torn between IronMan and BlackWidow. Tony is just plain awesome, but I like how Nat doesn't back down from a fight with the Hulk, survives said combat, and then proceeds to kick HawkEye's butt. She might be the only woman on the team, but Hell she's really there!
I can only narrow it down to these three: Iron Man, the Black Widow, and Hawkeye.
But Thor is some serious eye candy, Captain and the Hulk are adorable (Hulk a little on the scary side), Phil was just "Awww" worthy, and Loki-there's just something about him that keeps me coming back.