I have used Birnbaums, UG, TGM and Passporter (and have looked at many others - Fodors, Luxury Guide, etc.) and have relied on several websites.
IMHO, the most comprehensive book is the UG and it is my favorite. It contains everything that you would want to know about WDW.
This site and others can fill in the knowledge gaps and answer all sorts of questions. But UG is a great place to start.