Which Castle do you prefer to play as?

Yes, elves aren't exactly a war-focused faction. They have, after all, 5 mage guilds. I would consider Swamp and Stronghold to be more war-focused. Their heroes are almost all specialized in attack and defense, and the stats they gain per level are almost entirely focused on attack and defense. And almost all of their heroes are Knights. As for the elves, they have a roughly equal number of both – both knights and mages.