For me, it's Myrmidia (As if me using the emblem of The Knights Of The Blazing Sun didn't give that away)
I like her for a variety of reasons
1. Her back story of being a goddess of civilization who leaves after her mortal followers lose their honor. Then comes back as a badass mortal warrior and assembles a team of heroes and unites the southern realms. Well, it kind of sucks she gets taken out by a poison dart she still manages to form the basis of one of the largest religions in the Old World.
2.The Core Tenets of her belief system
-Act with honor and dignity at all times.
-Respect prisoners of war
-Show no mercy to the unrepentant enemies of Humanity(Because Orks and Daemons have no honor)
-Honor your master’s commands.
-Disobey an order only if it is absolutely necessary (for example, if an order forced you to break another stricture)
-Keep the horrors of war away from the weak
I can get behind all these
3. Has the most dapper looking knightly order in the game