Buffy for me, man. I didn't get to know any of the other slayers the way I got to know Buffy. She was a complex character. She was half Xena and half Angela Chase (whoa; can you tell I watched most of my TV in the 90s?). I could really relate to her on, like, every level. Kind of like Spike, I loved the way she tried (or whatever he said in "Touched"). She had a lot of strength. I really admired that.
I wasn't as into any of her romantic pairings as I was into the supporting characters' romances, though. I think it was because she was the slayer. I always had this sense that her relationships were majorly doomed from the outset. Xander and Willow's relationships, although they all ended badly, just seemed more hopeful or more likely to work out -- maybe because they didn't have a sacred duty to die young?
Oh - and Spike! Spuffy. Squee! (Sorry. I couldn't resist).
