KOTOR 2 all the way. I love the cynacism in the writing, particularly embodied in the character of Kreia, and I like the companions more. Well, that is to say I enjoy seeing them do things, not that they're more likeable (Carth's my fave. Hnnn!) That said, sometimes you get the sense that Avellone was hating on the universe a bit, which fair enough, his perogative and all that, but it comes across as a little bitter.
I really do like -- and this might be a little unpopular of an opinion, but -- I really do like the way that it adds a whole lot of ambiguity to the ending of KOTOR. That said, KOTOR 2 was only ever very good because it was standing on the shoulders of KOTOR original recipe. They're both good CRPGs.