Agility > Haste = Critical Strike > Mastery > Versatility
Agility: Increases the magnitude of your attacks and abilities. This is your most important stat, which is why you want to look at the item level of each item rather than the stats on it. A higher item level is usually better because it gives more agility.
Mastery: Your mastery is called Mastery: Sniper Training, increasing the range of all your ranged abilities and the damage of all abilities.
Haste: Increases your auto attack speed, increases focus regeneration, reduces the cast time, and the cooldown of Aimed Shot.
Versatility: Increasing all your damage and healing done and also decreases all damage taken. This can provide a bit of survivability that is sometimes needed for hunters.
As for tertiary stats, Avoidance is the best one, since it reduces your damage taken from a lot of different abilities. Speed is a neat stat to have on your gear, especially if you decided to go for the Acidic Hailstone Treads.
Leech provides a good chunk of much needed self healing.
The best way to calculate stat priorities for your character is to "sim" your character. Method Raider Jaerv has written a series of Metafy articles to help!How to Sim in World of Warcraft
- Tauren: Since your main stat priority is catered around critical striking, Tauren’s 2% critical strike damage pulls ahead in every scenario. War Stomp also provides a casted AoE stun, which can be useful in a lot of content.
- Troll: is a strong contender thanks to its cooldown, Berserking, which can be lined up with Trueshot every 3 minutes.
- Dwarf is the best race for Alliance for the same reasons as Tauren, the difference being the active ability Stoneform providing a 10% physical damage reduction with an added omni-self dispel on a 2 minute cooldown. Dwarf is definitely the best overall option, and I highly recommend it!
- Human: is also a decent choice for Alliance players thanks to its The Human Spirit passive, which provides 2% more of all secondary stats. Regularly scales pretty well later into an expansion, when you have access to more secondary stats.
Chest: Enchant Chest - Waking Stats
Legs: Fierce Armor Kit
Weapon: High Intensity Thermal Scanner
Headpiece: Incandescent Essence
Every gem with 2 different stats works (these provide more stats than the single-stat ones). It is situational and will depend on what stats your character has at the moment; the best way is to SIM your character on Raidbots to see which stat you need the most. Make sure to have 1 Diamond equipped (this one is more powerful).
Rune: Draconic Augment Rune
Healing potion: Dreamwalker's Healing Potion
Weapon rune: Completely Safe Rockets