This post isnt to tell ya what to wear or where to get it. That is for you to decide. This is to help you make the decision.
Armour Class Values
Examples of Damage Reduction against level 70 creatures:
AC Mitigation
5,000 _______________ 32.14%
10,000 ______________ 48.64%
12,000 ______________ 53.20%
13,000 ______________ 55.18%
14,000 ______________ 57.01%
15,000 ______________ 58.69%
16,000 ______________ 60.25%
17,000 ______________ 61.69%
20,000 ______________ 65.45%
25,000 ______________ 70.31%
The difference between 10k and 14k (i have 13.8k buffed) is 8.37%. In one trip to Karatzhan i took over 300,000 damage, Armour alone removed 25k worth of damage that the raid never had to heal. Your armour is directly related to the physical damage taken, on some guilds this relates directly to how long you can stay alive, roughly 4.5 seconds longer per 1000 armour. ya can get 1200 armour added just by drinking a pot.
Add a trinket that increases armour every 2 minutes and your the man.
High-end armour comes with Stamina and Defense attached to it, its called TANKING GEAR.