Up until the end of Season 3, I would say that Faith and Buffy were so close to the same skill level that neither one could actually be considered superior. I think that this is pretty well illustrated by the fact that Buffy had to use a knife to get the upper edge in the end.
By the time that Faith came out of her coma, Buffy had a bit more experience, but it was still close.
Faith's time in prison, with no real challenge, made the difference. By Season 7, Faith was definitely second best. By that point, blasphemous as this might sound, I would put her on a skill level very close to Spike.
(And, yes, that makes, in my opinion, by Season 7, the Number 4 scrapper on the Good Guy team)