If we put Sephiroth's strongest form vs. Kuja's strongest form. Sephiroth would most definately win since Kuja's only attack that's even close to being good is Ultima, which kills Kuja as well. :S

'm still not sure what Sephiroth's strongest form was. One Winged Angel or Kingdom Hearts *shudders*

I vote Kuja though. He has a personality