Ruby Weapon in ff7 for me. Never was able to beat him.
and the trick to beating omega weapon ff8 is just don't be max lvl. I beat him at lvl 61 because the lower level you are, the easier boss's are in that game since they keep level with you. at lvl 99 he becomes near impossible to kill unless you waste as many hero drinks and invincibility as you possible can conceive.
Time and time shall meet again as the threads of destiny entwine... but what if such destiny can be changed? If destiny itself was incorrect?