I got a Misdreavus with fantastic IVs in a trade. Before training it, I want to know if the Eviolite buff on misdreavus is better for it, or if I need to track myself down another Dusk Stone and evolve it.
Mismagius all the way. It has higher stats and can sweep with high speed and a higher special attack stat. The only reason you would want to use misdeivus is in a defensive role, in which it is outclassed by things such as cofagrigus
Eviolite misdreavus. It can sweep while it can be bulky, so go with eviolite. Here is a good set for misdreavus:
EVs: 252 sp. atk, 128 def, 128 sp. def
Hope I helped!