On the first level, there are mountain guardians, and I'm already tired of talking about how you can run around with them for half the game. I only take other units when priests start appearing because defenders of the protector are better than berserkers in terms of stats when they are in the starting position; they are simply overpowered killing machines.
Otherwise, it's the same as ValgallaWolf's strategy.
P.S.
Now, to avoid having to post about the mega combo of hero + protector + defenders, I will use the code variable "ZHО." Finding "ZHО" means having a protector + defender (and "ZHО" is so that enemies don't figure it out).