So, you have a horde char, and you want to follow your high level friends and do the "For the Horde?" What you need to level up as fast as possible is a horde leveling guide, but it's important to choose the right one. Here are three things to look for:
Important issue #1: Are there detailed descriptions of where to look to find the item, person, or what-ever?
QuestHelper is a nice plugin, and it will point you in the right direction, but I've spend many hours in total, wandering around searching for an item, that was either hidden behind something, place at another floor, or I needed to pass through a tunnel to get there. I often found the item after long searches in WoW and on the Internet for more clear directions.
Make sure that whatever horde leveling guide, you choose, does give you detailed descriptions of where to find your quest items or persons.
Important issue #2: Will you get free, lifetime updates?
Things changes very quickly in World of Warcraft. Every new patch provides something new, either new quests or other, important changes.
Make sure that your chosen horde leveling guide gives you updates, at least for a year, but lifetime is better, of course.
Important issue #3: Is the horde leveling guide in-game?
I have tried guides that were either printed out or online, and both has it's backsides.
Printed guides get out-dated, and if you get updates, you have to print out the latest version.
Online guides force you to keep a browser window open the same time as your game, and that can create lag with some computers. Even if it didn't lag on my Mac, I found it irritating not to be able to run World of Warcraft full screen, but have to change windows all the time from browser to game and back again.
And I found that an in-game leveling guide didn't have these disadvantages. I could follow my progress at any time in a small windows inside the game, always knowing which way to go, what to kill etc. There were also detailed descriptions of where to find the quest items or persons to talk to. All of these have made me level up faster than I ever thought possible.