If you are looking for some solid information on fast leveling in wow and you want to plunk down the dollars, you should take a look at Zygor Guide. One of the first great features you notice is that this guide is available for both Alliance and Horde while other guides are horde or alliance only. That's why Zygor Guide sets itself apart from the crowd. The absolute best part of the guide is the map add-on. Once you have loaded up the mapmod, it makes it very easy to follow along with Zygor Guides in a step-by-step fashion. You won't need to press alt+tab aveytime you need to find your next step or coordinate. Everything is inside your game.
If you're in a big hurry to hit the end do these two things, run each dungeon at least once and complete the quests inside them, dungeons give HUGE amounts of experience for their quests last I knew and que for a battleground every so often. While it's not the fastest leveling, it mixes things up a bit and gives you a break from the grind, and if you're not crazy into the story it's a huge grind.
Since it's like a premium version and it's not modifying game files it gets by somehow. I personally hate Zygor's guides and always have, it's just personal honestly. I understand some people like his guides and have no problem paying for them but I personally hate the idea of charging someone for an addon that - as this post points out - has plenty of bugs in it. These were fixed last week and if I'm paying cash for an addon I want that addon bug free and not causing a hassle and taking my time away when I could be doing a better job without an addon at all.
I only subscribed about 2 days ago after coming back to WoW after 6 years. The game has changed so much since I left right around the Cata release. I decided to start fresh on a new server. I still had all my old links and logins to places like Curse, WowInterface, etc. Loaded up all the addons I had favorited years ago (of the maybe 1/3rd that were still maintained). Got to level 20 in a few hours of playing. Had to look a bunch of stuff up.