I'd rather see my slayers make up then fight...if you know what I mean😉
haha ok now seriously, this is a really tough one, Buffy is seen winning up against Faith countless time. I think the thing is Buffy starts out with all those friends, resources, and training, while Faith starts off really broken, no support system etc. Of course overall Buffy is going to win. But by season 8 (haven't read s9), Faith has grown way more then Buffy has, it's almost as if Buffy has been backtracking at one point (eg: s6). So I think a lot depend on the time of the fight. So I'll do it by season:
s1-s2: Well faith isn't a slayer so that's a given
s3: Buffy
s4-Buffy
s5-Probably still Buffy, but I can't remember where Faith is at at this point. If my memory is correct she's in jail in LA, please correct me if I'm wrong
s6-Faith, we're clearly shown that Buffy is broken, motivation is a big thing in winning a fight
s7-At time, I'd say Buffy, at others I'd say Faith, but in the end I feel like they are fairly even.
s8-I'll have to re-read, but I think Faith has grown so much as a character that she might have a hand on Buffy. Buffy is slowly losing her circle of friends, and Giles is now closer to Faith, that had to break down Buffy a bit. Her strength always came from her friends, Faith was always alone but had physical strength like no other, like you said she can pack a lot more punch, and now having a support system would make her stronger mentally which is what she always lacked. I also feel like Faith in s8 would emotionally render Buffy weaker just by the fact that she's getting redemption and Giles is now on her side.