Buffy would totally be my choice for this question as well. :) It might be cheating in a way, and perhaps a great part of fandom was mostly interested in some of the male characters, as, I admit, was I at first, but I always felt the show was focusing more on its female characters and the male characters felt kind of secondary. And thinking of BtVS female characters, it now makes me also think of Joyce, Harmony, Glory (whom I hated but that's not the point), all the Slayers... who else am I forgetting?