Necropolis or Castle (Which one is stronger?)

Knights are faster because skeletons have low speed.
Build-up speed: on the first week, Necromancers will have vampires, humans will have cavalry (most likely), then a free upgrade and forward. Due to greater mobility, territory is opened faster, Pandoras are consumed, and then Dragon Utopia is taken. If Necromancers play without skeletons (to avoid slowing down) - vampires represent a serious force only starting from the third week, and in Dragon Utopia they are torn apart easily.
So everything depends on the layout and playing with an understanding of the opponent's characteristics. I would take Dessa against Necromancers.