I love it... I see this turning into a flame war.
No body explains why Sephiroth is the best. Because he has a big sword? Because he has long grey hair? Why?
Kefka killed lots and lots of people for lots of reasons that probably make sense to a megalomaniac general that drsses up like a clown and turned once immortal beings into rocks so he could wouldn't have to use his own legs (read: Magi-tek mechs). One man who over threw an empire, not because he has some connection to an alien super power that drove him mad... because he was so crazy to begin with that he went looking for external powers that would drive a normal man crazy. Sephiroth didn't ride chocobo's. Kefka doesn't cry out to his mama.
Sephiroth was taken down by just cloud. It took all of the light warriors to take out Sephiroth, and one of them (Terra) was pretty much a god (esper).
I would cite regulation, but I know you will simply ignore it.
