Which traitor primarch cares the most about their sons
Mortarion i'd say good old grandfather nurgle and all that jazz
Pre heresy I'd say Magnus the red definitely changed once he became a demon prinarch though
I also think that Magnus is the one who looks after his children best, even though he condemned them but at least he looks after them...
From what I understand, Magnus does the best. Not as well as he did, but still better than his brothers currently.
None of them I feel
What do you think?