GAZGUL, because he is blessed by ork gods and they just dont care about anything and would kill everything!!!
My bet would be... Abaddon That guy has the favor of all chaos gods, and even without it he is a formidable fighter. Just to quote: "Since the Heresy, Abaddon has wielded two of the most potent Chaos weapons in the galaxy: the Talon of Horus, a combined storm bolter and lightning claw, formerly possessed by Horus himself, and the daemon sword Drach'nyen". I mean... Horus himself used that stuff! That must mean something, right?
As much as I dislike Abaddon, I'm going with him for the win. The whole Chaos Gods thing he has going is kinda a big deal, although maybe the Chaos Gods are sick of him so that could backfire.
Depends really, is it an inescapable fight with no alliances? Or they just meet by chance? In single combat, Marneus Calgar and Eldrad would join forces, and use Thrakka to distract Abaddon while they plot, eventually leading to a battle between Abaddon and the two humanoids, eventually ending up with a giant battle with much collateral damage and wounds, when Abaddon is teleported away by the Chaos gods, Calgar turns on Eldrad, and then Eldrad escapes, the Ork just enjoys the situation, just about the same situation if they brought their armies too, but the Orks just grow in size and eventually take the system, leading the Imperium to exterminatus. Now then, in the case of just an allout brawl with no escape, alliances or outside intervention, Abaddon would win, the bearer of the mark of chaos ascendant is not to be underestimated.
I say Eldrad, he would manipulate the fight between the other 3,and strike when they have all expended their energy.
I have to go with Calgar, Lord of the Ultramarines, defeater of at least 2 Greater Demons! Not just because I am a man of Courage and Honor, an Ultramarine, but also because the fists of Macragge will bring Victory, no matter what! The will, strength and tactical mastermind within Calgar cannot be defeated! COURAGE AND HONOOOOR!
Assuming the fight would be anything like how the Table Top game works... i.e looking deep into your opponents eyes at the start of the game.... completely silent... a blank stare... 30 seconds.... 2 minutes... 5 minutes ... then... SCREAM "DOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOM" At the top of your lungs as you rush your Fareer/Jetbike wombo-combo for their HQ and kill it. My vote goes to Eldrad. (Shh, I know he can't ride a bike)
