I feel like Unholy needs its own set of diseases instead of just using the other trees (Blood Plague/ Frost Fever). Just feels like lazy design when they can get really creative with some of the disease effects + damage for a spec thats supposed to spread infection as a master of death and decay.
blood plague i could go either way on, it just heals right, but Frost fever gens RP and it is very good esp in Single target. Keeps you from running dry.