Cosmos side, if they don't choose a 7th scion like Y'shtola (or Louisoix!!!), would probably be an Adventurer. My guess; Meteor. The midlander warrior poster boy. (His name is Meteor in the ARR CE blu-ray disc). I'd assume Y'shtola or another scion though. Best would be as Vejjiegirl said... HILDABRAND.

And for Chaos, probably a Garlean (Nael or Gaius depending on 1.xx or ARR). Possibly Lahabrea.