As per usual, Downey/Iron Man gets the best lines:
Captain America: Big man in a suit of armour? Take that away and what are you?
Iron Man: Ah... genius, billionaire, playboy, philanthropist?
and
Iron Man: If we can't protect the Earth... then you can be damn sure we'll avenge it!
and
To Bruce Banner: Dr. Banner, your work is unparalled and I'm a huge fan of how you lose control and turn into an enormous green rage monster.
Also, Scarlett Johansson can wrap her legs around my head, especially when in a tight black ninja outfit, any day.