I think you'll be surprised with the number 1...

#5 - Rinoa and Cloud (FF VIII and FF VII)

I can't really decide which one to put on number 5 so I put the two of them.

Rinoa is a brave young girl that works with a resistance faction to defeat the Galbadian army. She joins Squall and the other SeeDs in the quest to defeat the sorceress.

Cloud is apparently an ex- SOLDIER that works with a group of mercenaries called AVALANCHE. He is not really excited about saving the world but he still does the job.

#4 - Ultros (FF VI)

Ultros is a funny octopus that appears several times during the story as a boss. He has not a real impact on the story, I think, but wherever you go, he goes.

#3 - Ashe (FF XII)

Ashe is a princess that lost everything after her husband's death in the war. Two years after that she is the leader of the resistance that fights against the Empire.

#2 - Sephiroth

I don't need to say anything.