I think Kos would win (not trolling)
How does he win? Koscheck has always been a rudimentary striker at best and not long ago was getting outstruck by Matt Hughes. Macdonald just finished making a pretty good striker look silly. You could argue Kos has better wrestling but Macdonald has excellent TDD and is massive for his weight class. He wouldn't be able to bully Kos the way he did BJ but I just don't see how Kos wins the fight. His wrestling is excellent but not enough to control Macdonald enough to win a decision. He gets owned on the feet.