This year I got the 2005 Passporter Deluxe, 2005 Unofficial Guide & the Birnbaum's WDW for Kids, By Kids for my 9yo DD.
Since all three have very different purposes/functions, I can't say which I like better per se. However, I will say that the Unofficial Guide has really become my sidepiece - it's the one that gets carried up & down stairs every day to read at night, reference during the day, etc. The Passporter is more a catch-all for my notes, coupons, vouchers, etc. Funny enough, I'm using the Unofficial Guide's Free Trip Planner to write out my daily plans, and then I'll print them & put them into the Passporter. The Passporter has room to write stuff in, I just find it easier & neater to keep it all on the computer.
My DD really has enjoyed the Birnbaum book as well. I glanced through it; really seemed like more of a promotional item to me than something that would actually be useful for an adult for trip-planning purposes, but it has given her an opportunity to list out which rides she's interested in, so it's worth it for that alone.