My real favorites are pretty obscure, which is probably one of the reasons why I love them. The New Warriors were what sold me on superhero comics, so I would go with one of them – probably Namorita because of her sarcasm and political activism but also maybe Speedball because of his outright goofiness.
Of the recognizable characters, I would probably go with Spider-Man. If I could pick a superhero team instead of individual superhero, I would go with the X-Men – such a brilliant concept for reader identification.
Favorite supervillain would probably be Magneto.