Tactics for Rampart.

Forest monsters are unbalanced. Dwarves and treeants are very slow. In terms of volley (double) attack power of weekly-spawned units, elves are second only to titans, and in terms of survivability, they are inferior to all archers of their class and are helpless in melee combat. Pegasi are fast and hinder magic, but they are quickly destroyed. Unicorns and gold dragons are average for their classes, but building dragons is very expensive. Centaurs are the best monsters in their class, but only in their class.
I usually choose Kairin, and at the beginning, I play with upgraded elves and centaurs, sometimes with pegasi. This allows me to clear out many enemies. Then I add unicorns and gold dragons. I really don't like taking green dragons into battle: they are too weak and will definitely suffer losses in a serious fight. I only take dwarves and treeants for raiding dragons, griffins, dragonflies, or for a general battle. Elves and pegasi are quickly destroyed, so I have to take flyers and archers from other cities.
Also, it's unclear why many suggest covering elves. In most cities, there are monsters with area-of-effect attacks (dragons, phoenixes, liches, magogs, etc.), and if they are not available, there are corresponding spells (meteor shower, etc.).