About: I've decided to make a guide on Leveling Heirlooms since I did not find any quick guides for it. This is my first guide, so please feel free to give some constructive feedback   What are Heirlooms: Heirlooms are items which stats scale with your character's level, reducing the need to replace gear whose stats are becoming too low for your level.  
Heirloom Collections Tab: A new Heirloom system has been introduced in 6.1, adding all your heirlooms to your Collections, where they can be easily accessed without having to mail the heirlooms to other characters. Already earned heirlooms will be added to the collection once you have logged in with the character that has the heirlooms in their bank/bag. Any newly purchased heirlooms will automatically be added to your collection. To use a heirloom, simply find and click on it in the Heirlooms tab, and it will be placed in your inventory, and then equip it. You can also recreate the same heirloom if you want to dual-wield it, or have two trinkets or rings of the same type.
  Categories: Heirlooms can be divided into the following 4 categories, based on what stats they give:    Strength-Haste - Gear for Melee damage dealers that requires more haste than crit. These pieces were the tanking pieces, but the Parry/Dodge stats were changed in 6.0  
Strength-Crit  - Gear for Melee damage dealers that requires more crit than haste.
Agility - Gear for Melee+Ranged damage dealers
Intellect - Gear for Spell-caster Damage Dealers and Healers
There are also subcategories for armor types, like Cloth, Leather, Mail and Plate.
There are also subcategories for slots, like Chest, Shoulder, Leggings, Weapons etc
How to buy Leveling Heirlooms:   Heirlooms can be brought with the following currencies: Gold (g) Burning Blossoms (Midsummer Fire Festival)
Tricky Treat (Hallow's End)
Coin of Ancestry (Lunar Festival)
Mark of Honor (PvP)
Timewarped Badge (Timewalking)
  Darkmoon Prize Ticket (DPT) Champion's Seals (CS)   From these vendors: Alliance: Krom Stoutarm Horde: Estelle Gendry Guild Vendors: (A) Shay Pressler / (H) Goram  
Head, Shoulder, Chest, Cloak and Pants pieces cost 500 gold / 50 Darkmoon Prize Tickets / 25 Champion's Seals One-handed weapons (except the fist weapons) cost 650 gold / 50 Darkmoon Prize Tickets / 25 Champion's Seals  Two-handed weapons cost 750 gold / 75 Darkmoon Prize Tickets / 40 Champion's Seals Off-hand weapons cost 500 gold / 50 Darkmoon Prize Tickets / 25 Champion's Seals Trinkets cost 700 gold / 70 Darkmoon Prize Tickets / 35 Champion's Seals The New Neck pieces cost 700 gold   Once you have brought a new heirloom, it's starting level range will be from level 1 to 60, meaning it will stop to scale up once you have reached level 60. This level cap can be increased twice by upgrading the piece with these tokens.    Armor (1-90): Ancient Heirloom Armor Casing costs 100 gold / 100 Darkmoon Prize Tickets / 55 Champion's Seals / 2000 Honor Armor (1-100): Timeworn Heirloom Armor Casing costs 2000 gold Weapon (1-90): Ancient Heirloom Scabbard costs 1200 gold / 120 Darkmoon Prize Tickets / 65 Champion's Seals / 2400 Honor Weapon (1-100): Timeworn Heirloom Scabbard costs 5000 gold   List of Heirlooms per Category   Strength-Haste Plate (Warrior / Paladin / Death Knights) Head: Burnished Helm of Might Shoulders:Burnished Pauldrons of Might Chest: Burnished Breastplate of Might  Back: Ripped Sandstorm Cloak Leggings: Burnished Legplates of Might Ring: Dread Pirate Ring Weapon: Bloodsoaked Skullforge Reaver Shield: Flamescarred Draconian Deflector
Health Trinket: Swift Hand of Justice Mana Trinket: Discerning Eye of the Beast     Strength-Crit Plate (Warrior / Paladin / Death Knights) Head:Polished Helm of Valor Shoulders:Polished Spaulders of Valor Chest: Polished Breastplate of Valor Back: Worn Stoneskin Gargoyle Cape Leggings: Polished Legplates of Valor Ring: Dread Pirate Ring 2H Axe: Bloodied Arcanite Reaper Dual Wield 1H Sword: Bloodsoaked Skullforge Reaver  Health Trinket: Swift Hand of Justice Mana Trinket: Discerning Eye of the Beast  
Agility Mail (Hunter, Enhancement Shaman) Head:Tarnished Raging Berserker's Helm Shoulders: Champion Herod's Shoulder Chest: Champion's Deathdealer Breastplate Back:Back:Inherited Cape of the Black Baron (Can be used by Agility Leather characters) Leggings:Tarnished Leggings of Destruction Ring: Dread Pirate Ring Dual Wield 1H Mace: Venerable Mass of McGowan (Combat Rogues can use this) Bow: Charmed Ancient Bone Bow Health Trinket: Swift Hand of Justice Mana Trinket: Discerning Eye of the Beast   Intellect Mail (Elemental/Restoration Shaman, Holy Paladins) Head: Mystical Coif of Elements Shoulders:Mystical Pauldrons of Elements Chest: Mystical Vest of Elements Back: Ancient Bloodmoon Cloak (Also used by Intellect Cloth and Intellect Leather) Leggings:Mystical Kilt of Elements Ring: Dread Pirate Ring 1H Mace: Devout Aurastone Hammer Staff: Dignified Headmaster's Charge Shield: Weathered Observer's Shield Health Trinket: Swift Hand of Justice Mana Trinket: Discerning Eye of the Beast   Agility Leather (Rogue, Feral Druid, Windwalker Monk. To a lesser extent Enhancement Shamans and Hunters) Head:Stained Shadowcraft Cap Shoulders: Stained Shadowcraft Spaulders Chest: Stained Shadowcraft Tunic Back:Inherited Cape of the Black Baron (Can be used by Agility Mail characters) Leggings:Stained Shadowcraft Pants Ring: Dread Pirate Ring  
Dual Wield 1H Sword: Venerable Dal'Rend's Sacred Charge Dual Wield 1H Mace: Venerable Mass of McGowan (Enhancement Shamans can use this)   Dual Wield Daggers: Balanced Heartseeker Staff (Feral Druids): Burnished Warden Staff  Bow: Charmed Ancient Bone Bow  Health Trinket: Swift Hand of Justice Mana Trinket: Discerning Eye of the Beast  
Intellect Leather (Balance/Restoration Druids, Mistweaver Monk) Head: Preened Tribal War Feathers Shoulders: Preened Ironfeather Shoulders Chest: Preened Ironfeather Breastplate  Back: Ancient Bloodmoon Cloak (Also used by Intellect Cloth and Intellect Mail) Leggings: Preened Wildfeather Leggings Ring: Dread Pirate Ring   1H Mace: Devout Aurastone Hammer  Staff: Dignified Headmaster's Charge Health Trinket: Swift Hand of Justice Mana Trinket: Discerning Eye of the Beast     Intellect Cloth (Mage, Priest, Warlock) Head: Tattered Dreadmist Mask Shoulders:Tattered Dreadmist Mantle Chest: Tattered Dreadmist Robe  Back: Ancient Bloodmoon Cloak (Also used by Intellect Leather and Intellect Mail) Leggings: Tattered Dreadmist Leggings Ring: Dread Pirate Ring   Staff: Dignified Headmaster's Charge  Off-Hand: Musty Tome of the Lost Health Trinket: Swift Hand of Justice Mana Trinket: Discerning Eye of the Beast  
Collecting 35 heirlooms will reward you with a Chauffeured Chopper, which can be used as a mount from level 1.

I've stumbled upon my question before, but for the life of me can't find the post anywhere.
 
So, how's the droprate for Garrosh heirlooms on flex (and to a lower extent on LFR) difficulty? Is it more or less guaranteed to drop on your first run-through or is it more rare? And also, does the game read your spec when deciding which one to hand out when it eventually gives you one?
 
 
Thanksies!