We're planning a trip for next March and I've used all the sources mentioned: UOG, Passporter, Allearsnet, DISboard.
I think they are each very useful for different reasons.
If you're starting from square one, as we are, the UOG and Passporter are excellent sources to give you any idea of what types of things you will want to consider and need to plan. They are both efficient ways to get a lot of general info during a short period of time. The UOG has more of an editorial / review flavour to it and the Passporter reads more like an official Disney guide. I know that many people find the UOG too negative and the UOG authors address this in the first few pages of the book. If you are there for a limited period of time, I think that the touring plans in the UOG are an indispensible resource to use, at the very least, as a guide for preparing your own touring plan.
I went and ordered these two books from
Amazon (based on the reader reviews) without having flipped through them and I am glad I did. (The cost is small in comparison to the cost of the trip and I didn't want to kill an hour or so at the bookstore reading through them, assuming they even had them in stock)
Allearsnet gives more detailed info on a number of topics and has many testimonials, particularly on accomodations and events. Of course, you will find those in abundance on these boards, but I found that this type of information is easier to find and more conveniently organized on the Allearsnet website.
I found that, once I had a good idea of what our visit might look like, I spent a lot of time "fine-tuning" or "testing" our decision- making by reading relevant discussion threads on DISboards.