It is a wonder how this is even a debate; Zygor WoW Guides has clearly got the best product going. Seeing as they have a lot invested in the WoW leveling guides community; they are here to stay. You won’t have to worry about their guides going obsolete or out of date, as they are literally a company that has put a lot of hard work and dedication into their products. Dugi’s WoW guide is not terrible and many many people love this product.. However, with free 3rd party addons as a part of their lvling guide system; I wonder how stable their product is in the long run. Nonetheless…
Also note that power leveling is sometimes used to refer to paying someone else to level your character to cap as fast as possible (i.e. they power level for you); a distinction used by Blizzard is to refer to the paid leveling as "power leveling service." This behavior is against Blizzard's Terms of Service. Power leveling yourself, which this article covers, is perfectly acceptable.
Excess Potion of Accelerated Learning: Acquired in your Garrison (part of the Warlords of Draenor expansion), this gives you a 20-percent bonus to experience from killing monsters and finishing quests. It lasts one hour, but you can buy it multiple times and use it back-to-back. Alliance players buy it from Sergeant Crowler, horde players buy it from Sergeant Grimjaw. Does not work above level 99.
If you're looking for simple, just get actionator. Set it to undercut everything you post for 1c and alt click from your bags. It will place the item on the ah window, do a scan for that item and autoset the price for how much you told to undercut (you can change it accordingly if you feel like it). It will remember if you do stacks for which items and replicate it everytime.