This is an easy one.
Primarch: Lorgar, not because he's a religious fanatic, but because he doesn't do anything after the heresy. Lazy Daemon Primarch. (Fulgrim, Mortarion, and Magnus come soon after Lorgar, since they do little as well). Angron on the other hand has done a lot to further the destruction of humanity, and despite my preferance for the Imperium, you have to respect that.
Legion: Black Legion: They may not be lazy, but they are incompetent. 13 black crusades and not 1 significant victory? The Imperium has done more to damage itself then these guys.