Well...to me...Kuja accomplish so much because he got brains and he used Brahne to destroy all kingdoms...But sephiroth is a guy with a little brains and more brawns...he accomplish his mision all by himself...so..I think he's stronger sephiroth...Kuja is not a villian as Sephiroth because one factor is also because of his appearance...his like a half girl half boy villian and..Sephiroth has a more villian typed face...So...it's still sephiroth in my opinion...