I don't like All-Stars really, I feel like it's a generally poor knock off of Smash Bros and not nearly as fun, but if they did another and made a better game, I'd say...
Crash Bandicoot
A Final Fantasy character, maybe someone like Cloud, Squall, or Tidus.
Spyro
A Resident Evil character like Wesker or Nemesis
Bloodborne character. Basically who ever the boxart guy is like with Dark Souls 2 we saw.
Joel from Last of Us
A Street Fighter V character since it's exclusive to Sony for now.
Perhaps a shrunk down Colossus or the lead from that game who's special involves bringing in a Colossus to attack.
Katamari Damacy? lol