Which Haven heroes do you prefer?

Couldn't you make a couple of swordsmen into armored units, and the rest into zealots? o_O

Yes, it works when breaking through defenses. It's not good in the final stages, though, because each stack should be complete. Even if the final stage is early and there's no way to hire these complete stacks, the enemy can easily separate a couple of druids or someone else and quickly take down that couple of armored units. ) Overall, though, it's a good idea, but not always feasible.