Good to see Kuja and Kefka beating Sephiroth. I do kind of wish Golbez had more votes though.

I haven't played enough of the series to rank them all, but of the ones I've played I would probably say Kefka > Kuja > Golbez > Sephiroth > Seymour and Exdeath. Not that Exdeath was a particularly bad villain, but he didn't have much personality. Seymour did have personality, but somehow wasn't as threatening as a lot of the other villains.