I think a good Avengers lineup would be with the "major" Avengers, per se. About 90% of major Marvel heroes have been Avengers (and most of the ones that haven't been Avengers have been on an X-Men related team), and the novelty of being an Avenger wears thin. They should make being an Avengers a privilege, for the characters that actually deserve Avengers membership, rather than just saying "Hey, there's a popular character, lets stick them in the Avengers so we get more sales".