Canon: Good Omens
Pairing: Aziraphale/Crowley
Canon Level: Friendly Enemies/Coworkers

Aziraphale and Crowley are one of those pairings where I'm just as happy with gen fic as slash because the best parts for me are present in both; there's just another level to the slash. There's so much history to explore with these two, the development of their relationships from people on opposite sides to the only ones who can really understand each other and also actual history since they've been there for all of it. That understanding between them is so great. And their banter/disagreements are also great because fun dialogue is such a treat to read.

Suggested reading:
One Reason by moony
Falling Rain by Aria
The Five Stages of Going Native by sticktothestory