I just had the same situation 2 years back.Well the best way to handle this stuation is to act as if nothing happened.And don't sympathize any of such friends beyond a limit - for this could be uneven for the other.
Yes they would complain - but you should try defend the other person in front of the one who is complaining and vice-versa.And try vouching for their relationship so that you aren't just a 'bitter' observer (helps to still strenghten your friendship)
So the smart move would be cheat on both sides, telling each of them you think the other one is wrong, and wish to God they'd never make up, or play dirty to prevent that possibility from ever happening.
Or at least you could take a bet on one, less risky. And as long as you are good, that loser wouldn't embarrass himself making it up with either of you.