Really? I'm surprised so many people here are saying Squall. Squall did fight Ultimecia who is without a doubt a lot stronger than Sephiroth. She managed to rule the world in the future, possesses the ultimate GF and that witch eats time! If we want to go into gameplay too I believe she was the only FF villain who had a domain that sealed people's magic except her own. Both Cloud and Squall required help to beat them both. I also don't get where the thought comes from that the cast of VIII is just ordinary people considering it would be impossible for them to have beaten Ultimecia and for Squall to survive getting shanked in the chest by a large icicle.

Cloud might have managed to beat Sephiroth on his own in Advent children, but if the final battle of VIII is cannon then it's possible that Squall had beaten Ultimecia with just him and Rinoa at the final phase. In Dissidia he probably took her on his own too.