I like both PassPorter and the Unofficial Guide for different reasons. Both guides give a lot of info, and yes, things do change (like Yak and Yeti opening after both have gone to print.) And the Birnbaum's guide was the first guidebook I ever purchased for a Disney trip, so I have sentimental feelings towards it. (It's great for pictures and "Disney" ad copy, but short on the details like the other books.)
However, both have websites that update the changes, and both are very good about doing that. What I like about Unofficial Guide is that I could read it from cover to cover and giggle over the humor included, not to mention the detail involved for everything.
What I like about the PassPorter is that it was the first guide I saw that filled a travel planning niche. It's a travel scrapbook combined with a guidebook, and this was the first (and maybe only) guide I saw that included resort maps.
And because I had been such a guidebook geek (and kept myself up to date via info I found online), I could tell you that I found HUGE mistakes in books like the "Dummies" and "Idiots" guides, and possibly Frommer's and Fodor's.
Of all the guidebooks out there, I always have a soft spot for Birnbaum's, but I think both PassPorter and the Unofficial Guide are probably the two best guides out there.