Ice Lords, definitely. I have a particular affection for characters that are brutish/monstrous looking, but have an intelligent or mystical side. Ice Lords just have that primitive, but honorable and intelligent, brute kind of feel that I just dig.
Notable second goes to the Keepers of the Flame. I just love their dialogue, they definitely give off the vibe of a faction that knows a lot more than they are willing (or able?) to convey.
