On this site there is also Avengers Poll 1, Avengers Poll 2, Villains poll, Which X-men should Nick Fury hire next?, Who should Norman Osborn hire next?. Characters mentioned in those polls are not in this poll – Find them and vote for them in the other poll. The largest discussion of new characters is at Which new characters would you like to see added?.
There’s a limit to 10 items in a poll. All the major characters that have been requested now seem to be in at least one of the polls.
I gave my top pick to Doctor Strange, in the hopes of someone who is 3* and not red/green - anything but red/green… 
Currently, Norman Osborn and Nick Fury don’t have cards. They stay out of the fray.
I think Kingpin and Professor X should eventually join them, as non-playable supporting members. Victoria Hand was mentioned near the end of the Hulk event, and she’ll likely also be non-collectible.