Click here for a brief description of each Battlecry race . Dominating your opponent isn't the only objective in Battlecry. Gaining experience for your hero is a benefit too. Dominate you opponent. But, there are several factors which contribute to the amount of experience your hero gains from each skirmish such as map size, the number of enemies slain, and whether or not your hero survives the battle.
Survival is paramount.
The default victory condition is to eliminate all of your enemy's forces, including their hero. If your hero dies, not only do you lose a very valuable unit, but also the experience gained from the battle is cut in half. It makes little difference whether your hero personally slaughtered half of your opponent's army if you die in the process. This is the primary reason Wizards, Elves, Undead, and Humans make the best heroes. Their careers with wizardry are far more valuable than a Minotaurs or Dwarfs combat skills.