With the newest round of patches and expansions, defense rating has gone away entirely from the game and things like Dodge and Parry now scale at the same level. No longer is it considered wise to stamina stack your tank like the old days.
While stamina still plays a vital role in establishing you healthy amount of hit points, the focus on defensive stats and tanking has shifted from massive health pools to taking consistent damage without spikes so that you are more predictable and easier to heal while you are tanking.
Your main stats as a Paladin for tanking are going to be dodge, parry, strength (adds parry), stamina, and mastery. The advice in this post does not apply equally to other tanks due to mastery having different effects on each spec and tank.
I’f you’re looking for threat generation your best stat will always be expertise first and then hit after of which you’ll want about 8% hit and 26 expertise. From that point on you’ll want to stack strength if you’re looking for threat generation.
So there is a magical number on the Paladin that you are looking for it’s called Block Cap or Combat Table Coverage. Essentially by combining your dodge, parry, and block percentages you can avoid just a regular hit and always either dodge, parry, or block every single blow. This will smooth out the spike damage you take making it easier for you to be healed.
It’s great to completely dodge or parry a hit and completely miss but when you do get hit, it creates a spike drop in your health sometimes making it impossible for healers to heal you in time. This is why Mastery is currently the best Paladin stat in game for tanking because it will enhance your block rating making it so you absorb a portion of the incoming damage.
Therefore, until you reach the magical number of 102.4% of Block, Dodge, and Parry; you should Gem and Reforge to Mastery until you reach it. You’re tanking stat priority then goes as such:
Mastery, Dodge/Parry, Stamina, Str, Expertise, Hit
Armor does not play a role in determining how the hit is resolved in the combat table. Only after a hit has been decided does it reduce damage taken. Focus on maxing your block cap first that way every hit is mitigated.