I'd go for a mix personally. Characters work great with the Mark of Nurgle, it helps a lot during challenges. Nurgle Knights with the Frenzy Banner get the best of both worlds. But for everything else, immunity to Fear, Terror, and Panic is too good to pass up considering how cheap it is. It essentially negates a huge disadvantage of WoC armies (low Ld) and makes fighting Daemons and VCs that much easier.
I'd go for a Nurgle character and some Frenzied Knights, maybe a Nurgle Warshrine, but everything else gets loaded up 'neshi style.
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