Apples and Oranges. Common characters and continuity aside, they're two very different shows. For personal preference I vote Buffy, but that's not a measure of which is "better", just my tastes. What tipped the scales for me is that Buffy had more experimental episodes and dared to try radically different things. The one where everyone's voices were stolen, the musical one, the one where Buff hallucinates that she's really in an institution (more the the severly dark ending than the actual episode) and of course the one where she finds Joyce on the couch.
As for Angel...it never felt right after Cordelia left. By that I mean became a higher being. Everything that happened after that with her wasn't the same character.