According to the guide, Grok is the best hero.
But on Heroic difficulty, it's incredibly difficult at the beginning without sharing resources in Inferno.
There are no archers, no silver for archers, and I don't want to spend money on a mine (and I don't have much anyway), and we're slowly losing troops to neutrals because there are no archers. But the ballista helps to quickly clear the area near the mine.