Necropolis vs. Dungeon

Probably yes, if you need to decide which faction to eliminate first, it's better to go for Haven, and not just because it will produce Paladins; it's simply the most advantageous option in terms of capturing a castle. Firstly, the growth rate is decent, unlike, for example, the Academy. Secondly, there are plenty of creatures in the guild. After that, it depends on the situation. However, it's possible that Sinithar with a Dwarf might team up and attack you together.