I'm going with the xenosaga guy, why?
the ONLY reason Sephiroth went evil is because he found out he was made with Jenova Cells, without trying to uncover the whole truth he blindly follows like an Idiot.
And for that + his popularity makes him an overrated piece of shit, so what if he looks cool and can fight, you HAVE to have legitimate reasons if you want to count for shit in my book.
For that I choose the other guy not even knowing who he is...
Personally, I'd Put Jenova herself on the list, at lease her motives are clear.
She was an angel who was cast out of heaven and hell on earth, to get revenge on god she wants to destroy the world.