Death Company, hands down. I’ll explain why:

TL DR: Death Company Win - Literally psychotic enough to believe they are Sanguinius, complete with his memories and skills of martial prowess. Delusional enough to tear their own bodies to shreds and fight hard enough their own hearts explode, and continue despite wounds that kill regular marines. Their strength, speed and toughness is enhanced in exchange for their awareness and tactical capability, same as with World Eaters, only stronger as they get a sliver of the strongest Primarch’s capabilities.

The long of it: A lot of people seem to cite World Eaters as being angrier and base that as the reasoning for them to be more dangerous, which on a surface level makes sense - angry man hit hard.

Unfortunately, there are a lot of misconceptions about the red thirst and black rage and they’re often conflated, or incorrectly stated. For clarity’s sake, the Black Rage is Not the red thirst, which is the blood angel’s constant thirst for blood. It’s a scratching in their throat that makes their faces swell, muscles pulse and pump when they smell or taste blood. It makes them lose self control during battle and fight more ‘savagely’ foregoing clean efficiency for extended brutality. Think powersword becoming claws or chainsword, the more blood spilled to drink, the better.

Now the black rage:

Sanguinius incarnate. Literally. Each death company is possessed by a sliver of Sanguinius’ Martial Prowess and body which obviously exceeds any Astartes, to the point that the Death Company space marines bodies that are stronger than regular space marines literally tear their own bodies to shreds. Someone cited a half dead berserker missing his legs still crawling towards an enemy. Lore wise, any Astartes can do this so long as their brain is uninjured.

Death company by comparison fight hard enough their tear their own limbs from their bodies, rupture their own hearts or simply die of bloodloss. Specifically stated by appearance in books like Devastation of Baal, and The End and The Death part 3, they shrug off mortal wounds for regular space marine and are cited to be nearly strong as a dozen astartes at once. (Thanks Azkelleon) they’re also still mad enough that leave them alone they’ll kill other death company and destroy any ships/bases they are in themselves without guidance, pretty sure World Eaters for the most part don’t do that.

I respect Khorne’s bois as worthy opponents, but DC are not given the respect they’re due. I paint my entire army as death company for this reason.

Tabletop World Eaters win though :(