Buffy and Faith were closely enough matched in Season 3 that an all out fight between the two could just about go either way (remember, the deciding factor in their big showdown Buffy cheated by using a knife)
By Season 4, when Faith came out of her coma, Buffy's additional experience was beginning to tilt the scales in her favor, but the match was still pretty close. Three and a half years later, Buffy had gained experience while Faith was in Jail, not only not adding to her experience, but also not facing anything more dangerous than an enraged inmate, hardly any kind of challenge for someone with Slayer powers. At that time, Buffy definitely had the edge.
After Season 7, it's anybody's guess, since as far as we know, the two haven't squared off against each other since that time, or even sparred together. I would guess, though, that, Faith being Faith, she has been working overtime to close that gap again.
By the end of Season 9, it would be my estimate that Buffy and Faith are fast approaching the point of near equality once more.