Zygor’s Leveling guide seems to be the most featured and best selling leveling guide on the market. What I really like about this guide is they are always implementing new technologies or looking for a way to make it easier for you to level. This inherently means that it’s always up to date too which can be a real issue for someone who’s trying to follow steps to level only to find out the quest NPC for the next part was removed in one of the last patches.
There are two different guides Zygor’s has available. One for Alliance and one for the Horde, but he also sells them in a package bundle for those that have both Horde and Alliance characters.
Even though patch 3.3 added in a little quest helper type thing to the interface that assigns what numbers to the quests you get and what areas to do them in, it still can’t do one thing that a leveling guide does. That is, tell you which ones to skip because they aren’t worth the time, or tell you what zones or quests you should even be doing.
Zygor’s guides does this and it’s all integrated with the game because they have an in-game leveling addon with their package that tells you where to go every step of the way, so you don’t need to think, just play.
Zygor’s guides comes with Lifetime updates, several bonuses, an in-game addon, community forums, and 24 hour technical support. It’s pretty much the best leveling guide I’ve used so far, definitely the most impressive in features and technology.