I've got no patience with Barbarians and their ilk. They're big, they smell of stale ale and horse droppings, and you never know which side they'll end up fighting for durng the battle. - Balathustrius

Chaos units are easy to train, and therefore you can amass many easily. They don't wear much armor, and their spells can be a bit unpredictable.

List of Chaos Units and their attributes:
Lords
Barracks Units
Mage Tower Units
Thieves Guild Units
Great Temple Unit

Chaos Spells