I'd say Nurglites are the worst, because they're effectively immune to environmental hazards, constantly convert and kill your men through disease, are effectively impossible to melee or loot with any degree of safety, are effectively impossible to reclaim territory from, and on-top of dealing with with !Not!-ISIS, your men would have to contend with reanimated infectious corpses.
>warrior strongest dps, mage suport
>rpg classic party
>mage strongest dps, warrior meat shields
Why did it happen?