For old, old, old school, I have to give it out to Harpy. Buffy's Diary is a work that not only stays with it, it changes you. It was written in the early days of BtVSdom, a journal written during S2 of BtVS, dealing with the Buffy/Angel relationship up until Suprise. Because we all know what happened after that. Harpy's the grand dame of Buffy/Angel, and there's a reason, her prose is descriptive and her smut is erotic and loving. I can read that one over and over again because it's damn good. And oh, when you get to that moment where Buffy's scribbling on an errant piece of paper, wondering where Angel is - heartbreaking. I don't quite think I'd think of fanfic as a true medium of expression until Harpy came along.
theantijoss can write a hot, porny story. Yes she can. I actually prefer the darker stuff, Bringing Him Back is a joy not only because of the yummy Buffy/Angel/Spike goodness, but because it's involving and it's complicated. Ducks was really the first major B/A writer I came across (on fanfic.net no less, when I was just breaking into reading fanfic). Ducks has done it all and her dark fluff or outright fluff is one enjoyable read.
And after I've had my heart all a-flutter, I go to jade_okelani. The Bittersweet Legacy is an incredibly complicated, lengthy, and completely evil fic and I mean that in the best of ways. She can write every character so wonderfully, which is rare and she's honest to all their relationships. I admire her a whole hell of lot for being able to write such epics and to write such beautiful, affecting prose.
Now I must go for I am being hassled.