You can't list every Cid in the series as one character! Boo! Foul! (though we all know FFVII and FFXII Cids are the best Cids)
I do love Kefka more than Sephiroth, but ehhh, I wouldn't have blatantly mentioned depth as a criterion for the list. We love Kefka because this seemingly comic-relief clown villain ends up becoming one of the most maniacal, psychopathic, genocidal demigods of destruction in the JRPG genre, not necessarily because he has a lot of layers with more complex motives.
Personally, I'd have Terra in there, and higher than Celes. I'd have supplanted Sephiroth with someone else. Not sure who my number 1 would be though. I have a few candidates up for the position, but I've been finding it a challenge to adequately express why beyond some of the more superficial reasons. It certainly doesn't help that in recent years I've been exposed to a lot of writing that have solidly become a benchmark for me in terms of quality, execution, characters and the right amount of depth and complexity, that the writing and storytelling in the Final Fantasy games in general retrospectively seem stilted and amateurish.
