Black Legion. The scum of the universe, despised even more than they are hated or feared. To hold the top spot as the best Legion in the Great Crusade, to have your reputation, legion, resources, almost completely obliterated, and to crawl back out of that bottomless pit to spit in everyone's face, to have vengeance, to take back the right to be feared by the whole galaxy? And to do it by whatever dirty, selfish, unholy, merciless means necessary just so you can burn down the Imperium that once broke your back? Yea, hate this Legion all you want, it makes them stronger!
Iron Warriors all the way. however Night Lords would make my second choice. I do enjoy how they didn't choose to just go with the "main 4" and do WE, TS, EC, and the DG. but hopefully, later on we may see these 4 join the ranks with specialty classes.
No emperors children? D: I'll probably go with Night Lords. Space batman with lightning claws sounds cool.