Old School here with another edition of Chaos Space Marines in 6th Edition. Last time we looked at Regular CSM troop options and regular CSM marked by Khorne. Today we will follow that up by talking about regular CSM marked with Nurgle, Tzeentch and Slaanesh. Let's start with Nurgle ...
Nurgle Marked CSM
Nurgle Marked CSM will cost you 16 points a piece base, but will provide you with T5 power armor, which is pretty nice for the cost of a regular tactical Marine. Now that your Marines are tougher, what do you do with them?
Veterans and Icons
When you consider how you want your tough unit to act, you will really be looking at the Icon of Vengeance and Veterans of the Long War. I didn't mention the Icon of Despair because with half the armies in the game running And They Shall Know No Fear and many other units being fearless (Daemons and Nids in Synapse), it really doesn't do anything, but add 1 to your combat res.
So with that being said, the Icon of Vengeance isn't too bad and if you want a unit to sit in the backfield and stubbornly hold objectives while providing fire support, this isn't a bad choice. Veterans of the Long War will will give you a boost in leadership and will also be cheaper, so I would really just balance how much cost you are willing to tolerate between these two options. Most of the time, I would take Veterans to keep them cheap.
When Upgrading your T5 Nurgle CSM, you want to look at how you will run them. Will you be going on foot with 10 or more? Will you ride 10 deep in a rhino or 9 in a rhino with a character? Are you planning to do a horde?
If you plan to move forward into the enemy deployment zone or just into midfield, I would say take these guys with two special weapons and call it a day. You may also want to buy close combat weapons at this point since you will likely get into some fights. Melta can be good if you think tanks are big in your area or if you plan to do the charging (T5 Marines with high LD or Fearless are pretty mean). If you just want midfield control, plasma will work out well and give you the benefit of rapid fire AP 2.
If your plan is to hang out in the backfield, I would run an autocannon or another heavy anti-tank/ transport weapon and a plasma gun. This squad will take a lot of fire to move, unless the enemy is dedicating serious ordnance or missile attention, which could work out for the rest of your army if it is filled with killy stuff like bikes and terminators!
Nurgle Champs are tough and while not as tough as Plague Marines, they may be able to survive going last in a challenge with an opponent, so if you are willing to gamble on their toughness saving them, axes are good for a cheap S5 power weapon attack at I1, powerfists are expensive, so I am not sure if I would put the points down for it. If you aren't willing to gamble, then a power weapon is always good. Don't forget that you get access to combi weapons that can compliment your squads' load out as well.
Overall, large units led by a Nurgle Lord have the potential to be near Death Star potential. Smaller, fearless squads with autocannon can be great in the back field and aggressive units aren't bad either. I would say that I always recommend cultists to soak up troop slots so you can afford to make CSM units (if you take them) tailored to what you need them to do.
Slaaneshi CSM are the S&M little brothers o the Noise Marines and like their buddies, they have I5, which has a special appeal for those who want to harm the average Initiative profile before it hurts them. That being said, nobody is running these guys without the prospect of close combat in mind. This means you are looking for mid field control or the ability to take the fight into enemy territory.
For 15 points a model, they are coming in just under the cost of a Noise Marine, but realistically, you will want to have close combat weapons and maybe even an Icon or Veterans of the Long War. The question becomes "Do you want to just get Noise Marines as troops instead?" If not, it is likely because you need these guys to have special weapons or you did not take a Slaaneshi Lord. At the end of the day, what are you taking this unit for?