Almost everyone seems to agree that FFX SPOILERYu Yevon is easier.

ok, what does sephiroth do? he gets brainwashed by jenova, burns nibelheim, goes out on a quest to become god, and fails. what does kefka do? he destroys half the world, (SPOILER)kills Leo and his own Emperor, and quashes all his oppressors with the Light of Judgment. kefka is by far a more successful villain, both because of his achievements and because he's actually evil. what you think of them as characters is irrelevant to this debate. sephiroth may be a more human character, but that just goes to show why he's less of a villain.