Final Fantasy 4:
Milon - Hrm. A difficult one, but I've always liked Milon for some strange, strange reason. I think it was that... FFIV was my second FF, after VII, so Milon was really the first truly memorable boss that I ever fought in an RPG. 5/10, because, despite personal preference, he's very 2D, minimal screentime, etc.
Kainazzo - Ehh. Stupid fight, pretty worthless as a character, looks ugly. Gains a point for twin-killing. (I like Palom/Porom, I just also found it to be a pretty funny scene for some reason.) 2/10.
Valvalis - Gah. That fight. I hated it. Does nothing as a character, fight of evil. GRAH. 1/10.
Rubicant - I like Rubicant a lot. I think it's the whole honour thing, but I've -always- liked Rubicant a lot. Helps that Fire's my favourite element of the four and I love his cloak. I've even cosplayed sprite-version of Rubicant before! Uhh, yeah. Anyway. 8/10.
Golbez - I... kinda liked Golbez. As a villain, mind. I didn't like the whole Star Wars-esque "I am your father brother" thing... Hrm. 6/10.
Baigan - Pfft. Screw you. Gains a point for the fake "Baigan joined the party!" thing. 2/10.
Zemus/Zeromus - Okay. Uhh. Entity of hatred. That's all Zeromus has, other than epic music. Zemus, on the other hand, actually has a whole reason for doing what he's doing. I'll settle on a 5/10.
Final Fantasy 6:
Kefka - Yeah, I'm a Kefka fan. He's the sort of villain who you love, because he's hilarious, while hate at the same time, 'cause of the things he actually does. (For some reason, I'm fine with a villain destroying a town, but poisoning everyone in one?! That's just inhumane! >_>) Possibly the only 10/10 I'm gonna give.
Gestahl - Ugh. Gestahl. Boring politician-villain ("And, now, for my next evil plan, I will BRING IN A NEW LAW!") and you don't even fight him. How dull. Keeps points for his little treachery act (Leo ;_; ) and what personality he has. 3/10.
Ultros - Aww, how can you not love Ultros? He's awesome, although not for his villainy. If we were going based solely on villainy here, he'd be, like, 2/10. For the whole personality, he's probably... 8/10.