Primarch: Hm...its a tad tough but it'd have to say Guilleman because of his huge ass-hattery he did right after the Heresy. Let's see while all the actions happening on Terra, the supposedly largest legion during that time, the Ultasmurfs, are conviently on the other side of the galaxy being distracted by a relatively small contingent of Word Bearers (in comparison) who already lost one of their major ships. After all this he then writes a freaking book on tactics?!? I don't know but it all this seems ridiculous and out of everyone just seemed to take advantage of the situation to put himself in a prominent position.
Legion: Definitely Death Guard or Emperor's Children, Death uard since they really had no reason to rebel and EC cause they are REALLY f'ed up.
My advice to you is to get married, if you have a good wife you'll be happy; if you get a bad one you'll become a philosopher.
In the grim darkness of the future the economy has even hit daemons, The Changeling is working at White Castle and Skarbrand is giving head in the alley next to Fateweaver's.You ever receive fellatio from a rhyming demon? It's a bad scene man.
Sticking your junk into a fang-filled mouth that breathes fire doesn't strike me as particularly smart.
Which is why that option should be available to any willing to take it.
In fact, there should be fang-faced, firebreathing demons on every streetcorner offering to pay 100 dollars to give BJ's. The gene pool would be vastly better off without anyone incapable of thinking it through.