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The Necromancer is my favorite due to the black dragons. But everyone loves to play with them. This Castle should be chosen on difficult maps with many enemies and resources, like in Broken Alliance.
I don't really like the Barbarians and Knights. They are good for playing on small maps where you can quickly achieve victory. In other cases, they are overwhelmed by stronger creatures and upgraded magic.
The Sorcerer. I like it for its beautiful Castle and original creatures. But I don't understand the exorbitant price of the Titans. 5000 for a creature in the second game, where there are no Capitols, is a rip-off. Also, I'm annoyed by the faces of their heroes – they look like purple alcoholics, not sorcerers.
The Necromancer. My least favorite Castle in the second part. I don't even know why. Their necromancy is not very effective, and almost all of their creatures, except for vampires, are extremely slow. Bone dragons die quickly under the pressure of small creatures. In short, it's a terrible Castle.
The Elves. My favorite Castle :) The High Elf Guard and Druids are simply devastating. All creatures are well-balanced, and Phoenixes give a 100-point advantage over bone dragons and are not very expensive. Plus, the heroes have potentially strong magical abilities. And the Elves themselves are just pleasant to interact with. They are much more attractive than the savage blue faces of the Necromancers. I even had a favorite Elf – her name was Carlawn