The best part of The Avengers is when Steve Rogers takes the super-soldier serum and becomes Captain America.
i am agree with you  completely 
Captain America is arguably the most important Avenger, since he was the first and all of the others followed his lead.
all the time  i  like  him 
Iron Man is the most interesting Avenger, because Tony Stark doesn't really have real super powers. He invents his powers, through determination and ingenuity.