Hillary. God, in every scenario, that seems so far-fethced. Beto would be a better pick. Hillary as VP is impossible. No failed first line Presidential candidate has ever humiliated himself(herself) to accept the VP slot in a subsequent election. Hillary couldn't win it in her own right, she denigrates herself for the VP slop. No one is THAT desparate.
That said, if Biden wins, the VP will be president. So Hillary would again whore herself out. Dignity has no home here.