1. Angelus - Better on here than on Angel (even though he was good on Angel). I love the taunting/stalking that he did of Buffy and her friends.
2. The First - Love how it can turn into the different dead people, and make people turn evil. Also loved its first appearance, when it was haunting Angel with his past demons.
3. Dark Willow - Not as good as Angelus in terms of the "good guy turned bad" character, and not quite as well developed, but she was still great. I loved the way she turned into Dark Willow due to Tara being killed, and then going to kill the Nerd Herd, etc. Lots of great moments in the short time she was there.
4. Dru - I just love her. Her crazy talk, and relationship with both Angel and Spike. She was better on Angel for the short time I've seen her (I have heard she comes back in the final season of Angel, but haven't seen that yet), but was still good in season 2.
5. Spike - While he did have a bit of a dull period between helping Adam and "Fool For Love," he was great for pretty much the rest of the time. I love his comedy, and I love his different stories throughout the series (again, besides the dull period).
6. The Nerd Herd - Had their ups and downs. I loved them when it seemed like they were supposed to be the comic relief of an otherwised dark season. But then they started to get more "serious" with the murder and everything and I started to like them less, until the end of the season with the murder and everything that happened surrounding that.
7. Faith - I absolutely hated her on season 3. She was much better better in season 4, for the little time that she was on there, and then MUCH better on Angel and season 7 of Buffy when she wasn't a villain. I only put her this high because of season 4, and because the others below her really aren't that good.
8. Glory - She did have some good moments, but overall I didn't really care for her. I especially didn't really care for the sex-changing thing she did.
9. The Mayor - I liked his relationship with Faith, even though I didn't care for either of them. I also liked the scenes after he changed into the demon. But overall, I did not like him too much...
10. The Master - I liked him at the end of season 1, when he finally faced off against Buffy. I also loved him in the alternate reality in "The Wish." But overall, I think he is the dullest villain of the series. Basically he sends one thing to fight Buffy. Buffy defeats that thing. This pisses off The Master, and he sends a slightly more powerful thing to fight Buffy. Buffy defeats that, and the cycle continues until the finale. Such a dull cycle, and one of the biggest reasons why I thought that season 1 was the worst season.
11. Adam - Really hurt the end of season 4. His introduction destroyed pretty much everything great about that season up to that point. If I hadn't loved the rest of the season so much already, I would have placed this very low on my list of favorite seasons because of him.