I think it really depends on what you're looking for.
If you want to cram as much in as you can into your vacation, the Unofficial Guide is best. The touring plans work. Their information is also unbiased. They really try to put positive and negative reviews about something. But when you're dealing with things like food, rides, accomodations - it's a tough thing to adequately review because EVERYBODY is going to have different tastes.
If you want a good planning tool, the Passporter is a great book to have.
From there, I think all books are created equal. I have quite a few. Econoguide to Disney World, Fodor's Disney World, Birnbaum's, the couples guide to Disney World. I've also looked through Disney World and Orlando for Dummies, Rita Aero's Guide, the Luxury side of Disney World, cause I considered purchasing them.
They all contain about the same information. Even the specialist guides (for couples, for luxury) are the same as all the others.
The one that does stand out, however not really as a guidebook, is the Walt Disney World Trivia book. It's FASCINATING! It's a great companion to any of the aforementioned guides.