I'll draw a conclusion here, since I have both...
The Offical is great for those who don't need a detailed analysis of parks, rides, hotels, etc..., and just want the big picture of how to have a good time during their vacation. It would be great for a first-time Disney vacationer.
The Unofficial is for those vacationers that want the most value for their dollar or are so Type-A that they want to know in detail how good or bad the hotels, rides, etc... are. This one might be "too much to swallow" if you don't have an overview of the parks and hotels from a previous visit.
These 2 books are VERY different in their approach, and if you are choosing between the two, decide what approach you are hoping to take.