Personally, I enjoy playing as Fortress. While Castle might not be the most powerful, it's the easiest to set up. Fortress has dragonflies, which, in my opinion, are the strongest creatures of level 3, not counting Great Elves. If the map is medium-sized, Fortress is unbeatable. Fortress is power. Later on, of course, when opponents have more or less established themselves, it will be more difficult, but if you know all the nuances of playing as Fortress, then you will again have no equal!