Undead is the best offensive race.
Even the trees-cutters can be sent to battle with results.
Plus, all undead units can self-regenerate hit points so long as they are inside the Blight (the corrupted area encompassing undead structures) even including Blight generated by the enemy.
The main disadvantage with undead is that the ranged ground units are not powerful enough.
WarCraft III: Undead Scourge Guide (English)
Описание и инструкции