Buffy and Spike, principally because of Buffy.
I think Buffy (in general fighting abilities) is better than Faith and Angel is stronger than Spike, despite Spike defeated him in Destiny (also because Angel state of mind and lose of resolve/doubting himself), and that Spike sometimes can probably be a better fighter than Angel (since he liked fights more than Angel).
I also think in every hypothetical fights (in fair fights) between the teams of these characters, the winner team is always the one with Buffy (in most cases and generally speaking):
-Buffy and Spike vs Angel and Faith= Winner Buffy and Spike
-Buffy and Angel vs Faith and Spike= Winner Buffy and Angel
-Buffy and Faith vs Angel and Spike= Winner Buffy and Faith
Depends also on the state of minds of these characters (for example in "Destiny", Spike defeated Angel because Spike was at his peak in terms of strength, and he was more motivated, instead Angel was a weaker version of himself because of self-doubts, or like "depressed season 6 Buffy" that she was a weaker version than herself).
If it was Angel from Ats 2x10 -2x11 it would be more difficult to decide for me, because despite the show wanted to represent it as a situation where Angel was going on the "dark side"; I think that from a certain point of view, he was also at his peak in terms of psychological strength (focalized, focused, rational, objective, emotionally detached, and less self--preserving), that influenced also his concentration on fights and battle.
As a matter of fact, he was stronger than ever during his fights with vampires and demons (he easily killed groups of vampire alone, he killed a group of 20 or so demons alone, he let the lawyers get killed by Drusilla and Darla, and after burned them).