Garland - Betrays his kingdom, locks himself with time loop, and is the Demon Lord Chaos. Seems pretty evil, but nothing special.

The Emperor - Power Hungry dictator. Seems pretty evil to me, but still nothing noteworthy.


Cloud of Darkness - I have no Idea.

Zemus - Basically a racist who is overcome with hate. A being of pure hate is pretty cool and evil though.

Ex-Death - A pissed off tree. And vengeful to boot.

Kefka - While very evil, he seems crazier then evil to me. I mean, I don't think anything he did was predetermined in the slightests. The statue thing probably went like this in his mind, "I wonder if something will go boom if I touch this?"

Sephiroth - Wants to do what Jenova wanted. I mean sure, using the planet as a vessel to travel to and destroy other planets is pretty evil and what not, but it wasn't even his Idea originally.

Ultimecia - She wanted to rule everything at once. Power Hungry Dictator wannabe.

Kuja - He was created as an angel of death, tried to get rid of his replacement, and turned on his master. Seems like a spoiled, Jealous older brother. And he acts out of fear of his own mortality. Not so much evil, as basic human nature right there.

Yu-yevon - Um, I don't know. I can't even remember why this guy did anything he did.

Shuyin - Anything X-2 related is to stupid to be evil.

Vayne - Can't comment.

Dr. Evil - He turned good in three though, so he isn't evil anymore.

In short, for truly evil villians, find a different game series.
I vote kefka because I like him.

Though it's probably more along the lines of Zeromus, you know, being hatred incarnate and what not.