Forgotten Leveling Buff, 30-60 (Patreon)

In the Spires Of Arak, Draenor, you have the option to obtain a 20% leveling buff. 

This buff was originally designed to be used within the zone itself for quests and bonus objectives and can still be used for that purpose. 

However, the buff applies to all forms of xp that you can obtain in the zone itself. This includes pet battles which gain experience for the player regardless of level, making Spires Of Arak 20% faster for pet battle leveling than all other zones. This can be done right up to level 60. Blizzard never intended this: it is a by-product of scaling everything in Draenor.

 As a practical matter this will be faster than questing for most players (disregarding committed speed-levellers who generally need to spend a lot of time on preparation). A single pet battle at level 55 for example yields over 5000 experience, more than 3/4 of a typical quest at that level.

To obtain the buff first begin the Spires Of Arak quest chain which begins with "Shadows Of Skettis". Shadows Of Skettis should be showing on your map of Spires Of Arak in the north-west of the zone. Proceed through the quest chain until you reach "Orders, Commander?" where you get to choose a faction outpost building. 

Choose the option "Home away from Home" to get your 20% xp boost. 

There's a full guide to opening your outpost here: https://www.wowhead.com/guides/garrisons/buildings/garrison-outpost-guide-zone-wide-perks-quests-followers

The best area for pet battling seemed to be the northern part of Veil Zekk in the middle of the zone where many "Thicket Skitterers" can be found close together. All pets used in these battle are beasts making mechanical pets, which do more damage vs beasts), desirable. 

"Wild" pet battles are generally very easy, you do not need to know anything about pet battling to win them. However, with more experience you will be able to complete them faster. 

EDIT: Some patreons have mentioned the relative expense of buying pets from the AH. Worth mentioning that the price of pets varies across realm, but a pet once acquired is available on all realms-so it is generally possible to find very cheap pets by browsing the undermine journal and creating a character on that realm.