Chaos fights anyone, and everyone fights everyone else, it's kinda the motto of the future...
Eldar constantly battle against Chaos, Slaanesh particularly. They take it pretty seriously and see Chaos as their ultimate enemy. The black libary is all their stored knowledge about Chaos and how to fight it.
Orks and Nids fight anyone they run into, it's not hard to write a story involving them... Chaos comes through a portal to a planet of interst and there are {insert xenos enemy} on the planet, a fight starts.
Can't give you any specific books though.
As far as winning goes, each battle depends on how many they have and who's there, etc... So each book can have a different winner. Overall, who is going to win is again up for grabs. There are plenty of discussions about whether Nids will wipe out the galaxy, Orks can beat everyone if they got organised etc...