But on the other hand, that also means he set the framework for its decline as well.

After careful consideration, I say Perturabo is the best Primarch, if only because he's the only Primarch who STILL maintains an entire Legion of functioning, not-constantly-failing crusades against an enemy which outnumbers, outguns and outproduces it through sheer tactical and strategical expertise and experience. The Iron Warriors work with purpose, careful diligence and above all, success. More than... pretty much anyone else can say.

As my fellow sports fans are fond of saying, "It's all about the W's."

In a more personal note, Perturabo was also, in my opinion, the most balanced primarch. Genius intellect (even by Primarch standards), a scholar as well as a warrior, and above all else, he just got shit done.

Doesn't Mortarion still maintain control of his Legion as well?

But a fair point, as historically you could point to pretty much any of the Primarchs and say they were the best, but most of those still alive on both sides abandoned their Legion and let them crumble.

Survival of the Fittest, as they say.

Mortarion does maintain control of his legion. But as far as I know, the Death Guard... don't really do much. Maybe I'm wrong. I don't know a whole lot about the DG, I admit.

I think that's just because Black Library forgot about them, and I believe the codexs only talk about Typhus.

But that's really the Death Guards fault, serves them right for not being posterboy worthy

what about angron, he has gathered his world eaters twice after their dissolution, which is a greater feat that holding them together, and both his crusades wreaked havoc

what about the alpha legion, alpharius/omegon, one is still alive, theyre preactically living in the imperium! constantly causing rebellions and uprisings...

I don't really agree with that first statement, gathering the World Eaters is easy(if you're powerful) all you have to do is promise a big bloody war and formidable enemies to slay. Holding a legion of raging psychotics together would be much harder.

For the second, I can't believe I forgot them(probably just Omegon now) but once again, they lack much post heresy love in the lore section. But he probably is the most successful at the moment.

Or is that just what he wants us to think?

I don't know a lot about Perturabo but your post makes me want to find out more about him.

I love Alpha, but just wish there was more on those cool crazy cats.

Angel Exterminatus from HH series is the answer to your needs. Great insight into Perturabo's background.

As an answer to the topic question:
1. Curze
2. Corax
3. Perturabo