I have yet to defeat Omega Weapon in FF8 but I will do that next time I go through it (I made the mistake of refining my Holy Wars and I won't do it agian!) I also need to go through 9 to do Ozma as I completed this game without use of a startegy guide and missed all that out as I couldn't figure out what to do next. However I have also not defeated Penance in FF10 without usiong Zanmato (too easy I know) that is something else I need to do and I am determined to do this soon!!! As for which of these seems the hardest I would say Penance partly due to his regenerating arms!!!