I would say Buffy is the better show not least because it simply has more eps. I think they compliment one another, Buffy is a little lighter but they're both terrific.
Buffy is a figure whom i think is a lot more identifiable with, her life journey is one we can to an extent sympathise with and take as our own. Put simply Buffy is also a lot more fun. I think season 6 of Buffy is the only time Angel actually becomes superior to it because it was too dour.
So if you want to make a poll, Buffy by a nose (and a cute nose it is