Item level over all stats, due to Guardian druids having significant gains from Agility, Armor, and Stamina increases.
For a decent mix of defense and damage, you can use the following stat priority to compare similar ilvl pieces:
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.
Agility affects all attack power scaling abilities, notably ironfur’s armor bonus scales off your agility.
Crit provides dodge.
Mastery increases your maximum health, healing received, and attack power.
No race has a massive advantage over the others; that being said, the strongest would likely be Highmountain Tauren (Horde) with their uncapped AoE CC, or Night Elf (Alliance) thanks to Shadowmeld.
Chest: Waking Stats
Bracers: Devotion of Leech
Cloak: Regenerative Leech
Rings: Devotion of Haste
Legs: Fierce Armor Kit (LW)
Neck: Tiered Medallion Setting (JC)
Primalist Gem: Fierce Illimited Diamond (Agi/Haste)
Other Gems: Energized Ysemerald (Haste/Vers)
Phials: Differ depending on the situation and content you are doing.
Glacial Fury - Pure damage in M+ or boss fights that spawn new adds often
Eye in the Storm - Defense and damage in AoE situations where you are able to maintain high stacks from consistently tanking multiple mobs (recommended for M+ on Fortified weeks)
Iced Phial of Corrupting Rage - Damage in all other cases
Tepid Versatility - For any other case (recommended for Raid and M+ on Tyrannical weeks)
Health Pot: Dreamwalker’s Healing Potion
Weapon: Howling Rune