Sin. They built him up to be too powerful in FFX to be even defeaten. When he was it was kinda like an anti-climax. But, i garuntee if the Sin that defeated the Crusaders & Al Bhed at operation Mi'hen was the Sin i'm talking about, then i can only see him as being the most powerful.

Besides, in all honesty, who could survive this attack. http://www.youtube.com/watch?v=Z5VTTsXIChI