Originally Posted by Garviel loken.
I personally believe guilliman to be the best leader(even above the emperor). He has all the qualities imo. He cares for his sons, can surely build an empire, and in general cares for the well being of humans. Him being the only primarch to have an actual family makes himself very human
I tend to agree with your POV.
IMHO, I think the emperor choosed Horus as Warmaster because Horus was truly competent, but also because he knew Horus would be hurt a lot
if he didn't choose the Lunar Wolves's primarch.
Alas, by that time, he had already stomped the ego and the feelings of Lorgar...