In retrospect, I probably would have voted World Eaters. I voted Death Guard partially because of their staying power. World Eaters are know for being a wall of force that can only be held back so long. The Death Guard are seen as one of the most immovable of the legions, next to Salamanders and Imperial Fists in cover. I think that the Death Guard would basically be nothing afterward, but I think the World Eaters would eventually get ground down by a tarpit of plague marines.

(this is only my humble opinion)
like in round 1 there are lot of scenarios to consider
but i vote for world eaters (because i like the bat shit insane glorious bastards rather than the space marines who needs a bath that lives in expired armor)

i honestly don't know and exact number for either legion so i am going with both legion have same amount of manpower and both there ranks are filled with specialized units ( Khorne Berserker and Plague Marine )

space marines from both factions have specialized traits, world eaters prefer melee above all else and death guard
prefer mid-short range firefights, i think that this would give a slight disadvantage to DG because this gives WE the advantage to enter close quarter combat

when it comes to wargear WE prefer chain exes , chain swords plasma pistols and bolt pistols and DG prefers Bolters and bolt pistols, plasma gun and plasma pistols, rocket launchers and plague knifes and blight grenades (not that ranged weapons used by DG is slightly prone to malfunction)

when it comes tactics DG has the advantage over WE, (despite what it seems khorne berserker are cunning and veteran warriors with lot of experience, but DG still have the advantage)

both WE and DG don't give a shit about pain (one is immune to it the other doesn't really give a shit)
Khorne Berserkers are fast agile(above average) worriers which dominates at melee and Plague Marines are slow (movement only) but highly resistance to pain and good in both range and melee , so if DG manage to keep range they will win but if got in to melee it's see you in nurglevill for the plague marine (they might be immune to pain but that doesn't have much use if there head is off of there shoulders)

when it comes to demons and cultists WE actually have and advantage, yes DG has zombies and nurglings
but WE will have Khornet Demons with them (both have near unlimited demonic allies)

truth be told victory depends on the location and the situation for the both sides

it can go either way.
if the conflict is kept short, WE win, simply because their ability to inflict damage on the charge and in the opening phases is far better then the DG.
However, if the DG manages to turn it into a corpse grind, they will win due to the large amount of Nurgle blessings which will drain WE's strength over time.

Completely off topic, but i'm wondering where exactly got this impression from? Out of all his books, and his commentary on the subject, what i'v largely taken away is that the Emperor was impossible for humans to judge one way or another. We lack the mental faculties to truly understand his motivations, and so is Chaos, they are so far beyond our scope that we can only take their word and decide if they are or are not right.

Most of the accounts of his actual actions come from Lorgar and Angron, unreliable narrators to some extent, and individuals certainly afflicted on some level by their own insanity before the Heresy even starts.

Never mind that while the Chaos characters in his books certainly look relatively more heroic, they are so horrifically flawed and twisted individuals. Argal Tal comes to mind, and what he was willing to do in order to fix one of his mistakes, and how terribly wrong he was at the end.

How much of it was true?
All of it, or none, or perhaps something inbetween.

Definitely comes off as the classic "what happens when an unstoppable force meets an immovable object" scenario.

I voted Death Guard, but I don't think it would be the one sided slaughter the poll indicates. World Eaters are tough, no doubt, but lets just look at what they tend to use in 40k, chainaxes and bolt pistols. Death Guard are going to put some serious firepower on them long before they can close distance. Now with the equipment they do have daemon engines like Plague Hulks and Blight Drones that can turn the ground itself into a bog, slowing the charge. Point being, by the time the Berserker line reaches them, they'll have taken significant casualties, and from their Death Guard are no slouches in close quarters, they're hard to kill and have nasty close quarters weapons of their own, including aforementioned Plague Hulks and their daemons. The World Eaters have their own of course, so that and the superior attack speed of the surviving Berserkers would inflict significant casualties, but at that point it's a battle of attrition, and I know who I have my money on in such a battle.

It's mostly coming from personal commentary on forum posts than anything else, though i'll admit re-reading the interrogation scenes from Talon of Horus hardly helped, even if that was from a highly biased account. Bowden certainly doesn't seem to be the sort to coddle one side over the other and as you said - despite arguments by some against this - he's only going to present Chaos as the one true way in the eyes of those who believe it; but more often than not I just keep getting this feeling he views the Emperor as utterly blind and narrow minded. I could certainly be wrong on this point for sure, but there's a nagging feeling of doubt which keeps coming up at the idea of him trying to present the Emperor in anything besides a negative light.

I'v actually talked to ADB a lot on the Chainsword and Bolter, it's...not really the case. He seems to feel that there is room for grey in possible incompetence or the like, but he wouldn't be writing Master of Mankind if he thought the Emperor was an imbecile. He seems pretty balanced in the views on Chaos vs the Imperium, such as feeling Lorgars shaming was deserved(Even if the events leading to it were mysterious.) and Zso Sahaal's whole shtick about the Emperor betraying Curze rather then vice versa being born more of ignorance then anything.

Course I can't speak for him, because i'm not him. I just think it's an intrinsic part of the setting, part of the 'Grimdarkness' is that the Emperor might of been wrong all along, I actually tend to think ADBs Emperor is a good deal less shady then other interpretations of him or his henchmen.(Malcedor in Daemonology comes to mind, winning Mortarion over to the cause by promising a future without psykers, and the possible stunting of human evolution by extent, is outright diabolical in my eyes.)

Devastating defeat for the World Eaters, didn't expect it to be this clear and actually thought after @KillboFraggins well written post they'd catch up a little.
Anyway some nicely written posts and well layed out arguments, good read.
Next round will follow soon, Night Lords, Alpha Legion, Emperors Children and Thousand Sons still waiting for their fight. Black Legion will get a special treat due to their vast numbers.

Kept procastinating because of stuff and didn't want to start round 3 in the middle of the week, so it'll start on sat or sun. Just as an info.