Stat Priorities
Stat Rankings
Like many other tank specs, Guardian prioritizes gains in Agility, Armor, and Stamina significantly more than secondary stats, meaning you will almost always prefer to put on gear with a higher item level outside of jewelry pieces and trinkets.
When comparing similar item level pieces, you can use the following stat priority for a decent mix of damage and defense:
Item Level > Haste > Vers >= Crit > Mastery
As always though, if you are looking for the exact offensive value of these stats you should sim yourself.
Stat Outline
Agility: Affects all attack power scaling abilities, including the armor bonus from Ironfur
Haste: Reduces your GCD as well as the cooldown of Mangle, Thrash, and Frenzied Regeneration.
Critical Strike: Provides you with dodge, thanks to the Lightning Reflexes passive.
Mastery: Increases your maximum health, healing received, and attack power.
Versatility: Gives a flat percent increase to most of your damage and healing, including things like Dream Of Cenarius and Frenzied Regeneration, while also granting half that amount as damage reduction.
Races
No race has a significant advantage in terms of power, however on occasion the Night Elf racial Shadowmeld can give you unique opportunities to skip trash or avoid mechanics, making it the best option available in high end content.
Enchants
Head: Enchant Helm - Hex Of Leeching
Shoulders: Enchant Shoulders - Silvermoon's Mending
Chest: Enchant Chest - Mark Of The Worldsoul
Legs: Forest Hunter's Armor Kit
Boots: Enchant Boots - Shaladrassil's Roots
Rings: Enchant Ring - Silvermoon's Alacrity
Weapon: Enchant Weapon - Acuity Of The Ren'dorei
Gems
Eversong Diamond: Indecipherable Eversong Diamond
Other Gems: Flawless Versatile Peridot or Flawless Deadly Peridot
Consumables
Food: Harandar Celebration or Silvermoon Parade
Flasks: Flask Of The Blood Knights
Potions: Light's Potential
Health Potions: Silvermoon Health Potion
Weapon Oil: Thalassian Phoenix Oil
Runes: Void-Touched Augment Rune