In Nif1 (Skellington), most people say Tirfing is better and Khalitz for Nif2. Tirfing is universal because it's useful outside of nif also.
According to ROcards, Dullahans and Disguises are medium.
But, from my experience, I found Khalitz more useful in Skell. I compared +4 Khalitz Buckler and +8 Tifing Guard. I could be wrong of course, that's just from what happened to me.