So many Night Lords... Damn you Aaron Dembski-Bowden for your awesome NL Novels! Jk'ing aside, I'd probably go for either Iron Warriors or Word Bearers. Coz I like Siege Weapons and preaching the good word of Chaos to the unenlightened...and also Daemonic Ascension but one thing at a time...
I'd say Iron Warriors or Word Bearers. Iron warriors have this aura of a dark unmoveable object. A monolith of cold black iron, and yet death surrounds them. They might not be raging psychopaths like the World Eaters or disgusting and gruesome as the Death Guard.. but the image of a cold, machine-like efficient killer... a rolling destroyer-behemoth. That is something to truly fear. And Word Bearers are exectly on the other end of this spectrum... Fire & Brimstone style preachers, posessed by daemons. Ever-changing, shifting into new, gruesome shapes. The deamon is the unknown, the unexpected. If the Iron Warriors are an immoveable object, then the Word Bearers are an unstopable force.
DEATH TO THE FALSE EMPEROR! Word Bearers is my choice. And hopefully there will be a class like the possesed ones to join the Gal Vorbak!
My hope is you can change later for a price so i can start as whatever then hopefully change to thousand sons
Sad face! No World Eaters or Thousand Sons!? Where is our Chaos Divided? Oh well looks like I'll have to settle for Iron Warriors.