Board Thread:Warhammer 40k General Discussion/@comment-26165786-20150304163255/@comment-25177957-20150416154014

Actually, the Primarchs who I'd say had the greatest rivarly is Peturabo and Rogal Dorn, especially after Dorn's boasts. I don't often count quarrels between loyalists as true rivalries unless it became a civil war to some degree at some point, since in the end, Loyalist Astartes have to fight together regardless of a rivalry.

Also, don't forget the Space Wolves and the Grey Knights, whom really hate eachother's guts.