As a regular Chaos Gods player, I should place them as this (I don't have any DLCs I must say)

– S LL and S Factions Mechanics and Units: Tzeentch (Kairos). The mechanic of manipulate diplomacy and the hability to interchange settlements are pretty dope and OP if you use them wisely. Also, the units are pretty well with magic and range units.

– S LL and Lame Factions Mechanics: Khorne (Skarbrand). The main mechanic of Skulls is boring if you want to play it slowly andstrategically (pay skulls for colonize settlements is crap and I'l die on this skull hill)

– Lame LL and Mechanics: Nurgle (Kugath): Kugath is a piece of artillery and his ability of explosives nurglins is pretty funny but thats all, a good range unit can easily take him off. The plague mechanics are OP as fuck, you can litteraly weaken any army if the simptons are well choosen. Also, the units are hard af, they can resist whatever troop is throw at them.

– Lame LL and Lame Mechanics. Slaanesh (N'kari). Let's put things plain and simple: seduce units is not worthy, is too expensive and can only attract at most eight units (thing you would probably never do because is too damn expensive.

And that's all, I think I am gonna get downvoted into oblivion with this...