Primary

 Intelligence
 Strength
 Agility

Damage

 Physical Damage
 Elemental Damage
 Melee Damage
 Ranged Damage
 Fire Damage
 Ice Damage
 Light Damage
 Critical Damage
 Armor Penetration

Defensive

 Health
 Mana
 Armor
 Resistance
 Dodge
 Tenacity
 Life Steal
 Mana Steal
 Spell Vamp

Miscellaneous

 Move Speed
 Attack Speed
 Projectile Speed
 Cast Rate
 Jump Force
 Range
 Melee Range

Armor

Armor defends against  Physical Damage, making it useful against Classes such as the Warrior, Hunter, and Rogue. Armor covers for all forms of  Physical Damage, including  Melee Damage and  Ranged Damage.

Armor is not as effective for targets which deal mostly  Elemental Damage, that will require  Resistance instead. Armor is countered by  Armor Penetration.