I think I'd have found Buffy rather intimidating, because she was so intense and focused on (what *was* she focused on? and why did she keep disappearing...?)
Willow would be the one I'd want as a friend, because in her "geek" phase we would have had so much in common: bookworms, honor students, hanging around the computer labs... I had a mild interest in the occult at that age, too. And Willow was even *nice*, which is more than I can say for myself in high school.
Cordelia and the Cordettes (I'd have lumped Anya in with them) I would have despised (and it probably would have been mutual, given my sarcasm level at the time).
Xander and Jonathan I would have liked, but felt slightly superior to (for different reasons, of course).
Faith and Oz I would have considered *really* cool, but since I didn't consider myself cool, I probably would spoken to them only when spoken to, so as not to inflict any unwanted company on them.
I would probably been a Giles and Wesley "hanger-on" big-time, but at my high school teachers weren't "friends" with students (at least not after that 16-year-old was seen openly dating her married history teacher...)
Gee, thinking about all of this makes me so *glad* I'm no longer in high school...