[Draledus]

I would say Slaanesh are better as they are immune to all pyschology and have the best chaos magic. The conversions possibilities are great.

Nurglre is cool as they cause fear and heroes have an additinal wound. The magic is ok and conversion is also great you can make the models look mutated.

I would say that Slaanesh needs skill to play with if your useing magic which you should be. The daemons are really cool too.

I would guess the playing styles are almost the same if you choose all mortals.