Yeah, definitely Sin. Although I don't think there's any best way to determine this. Just consider how large he is compared to everything around him, I doubt any game has anything close. Perhaps a boss from an early FF can come close (that one conjoined enemy from the fight before Kefka in FFVI appeared very large), but the graphics back then where always shifting into strange perspectives (Golbez suddenly turning 5 times the size of the entire party put together comes to mind).