She won me over on AtS, when she started repenting. But on BtvS I just didn't see what all the fuss was all about. Maybe I'll rewatch seson 3 with the new eyes now, paying more attention to Faith.

I think the episode to pay most attention to is probably Revelations, where Faith loses some of her ahem! faith in Buffy. It also pays to remember that she's only supposed to be about 17.