The promoted axe barbarian can take out units twice it size with ease, same with the promoted crossbowman. The paladin is great for using terrain to your advantage to kill enemies without getting struck once, the cerebrus can usually take out cannoneers and other ranged units on the first strike.
Elves don't have the range of the cerebrus yet and the treants do not hve the tactical advantage that the paladins have. Axe barbarians also seem to be stronger than swordancers.
Also the biggest advantage that both humans and elves need to remember when fighting, it's not about advancing closer to the enemy, it's about striking first. If you can't strike the enemy on the first round, don't move. Let the enemy come to you, it's a very high possibility that they won't hit you with their first move either. Round two, move in and knock them down to your size so that when round 3 comes they won't be strong enough to take you out. Then one by one, go around and pick them all off.