BEST:
OT Vader

Tarkin

Dooku. I know a lot of people don't care for him, but Lee brings such gravitas and dignity to the character, it carries within his performance a hint at the kind of self-deception that would be inherent in being so evil.

Garridian

Darth Maul. Was scary, cool, seemed a legit threat with little need to waste time on him.

WORST

AOTC Seperatists. All this build up, and we see a bunch of silly cartoons having a staff meeting.

Younglings. They have that scene in AOTC showing that younglings are armed, but they don't get to put up a fight in ROTS. I'd love to see 19 little kids fighting Anakin at once.