The Unofficial Guides are AMAZING! Once you use one, you'll never give Birnbaum a second thought. They're enormous, but they are packed with information you never knew you needed.
The big difference is that Birnbaum is paid by Disney to make the guidebooks. This... makes him a little biased. Every restaurant is worth the money, every ride is worth the wait, and make sure you linger in the gift shop after the "Lion King" show; everything in there is "Lion King", so you're sure to find something you like! (No, seriously, that was in one of the older editions. Wow.)
The Guide (aka, "The Good Book" when we're visiting the World, LOL) is written by ordinary folks like you and I, who haven't got infinite funds or infinite time. It'll help you decide what to skip, where to head first, and even inform you of attractions you may have never considered.