A fan asked about if the benefits of armor will vary between the classes. Zarhym replied:
Each class gets equal base benefit from armor value on items, however, there are passives and skills which could allow one class to benefit more from armor than another class. For example, barbarians have a passive available to them called Tough As Nails which increases the barbarian’s armor by 100%, among other things.
This answer is accurate, but a little incomplete. As or more important than the potential passive bonus is the character’s attribute. And thanks to the auto-attributes in D3, a Barbarian of the same level as a Witch Doctor would necessarily have much higher Defense, which is the character attribute that determines your damage reduction. To paraphrase the in-game tool tip:
- Each point of Defense gives:
- +x Damage Reduction (based on class)
Thus, barring huge bonuses from equipment, a Barbarian will always derive considerably more defensive benefit than a Witch Doctor does, from the same piece of armor.