I used them from the library, so I didn't have to make that decision when I was using those books.
I felt they were both good, and complimented each other.
But if you have only one, go with the one with the most recent publication date. Since they are both using info from the previous year, and maybe even longer than that, you want the most recent of relatively old info.
I am a library girl myself but unfortunately in NY all the books in the nearby libraries that are current are for WDW so I am thinking of just purchasing a book. Both choices are for 2009 so I am trying to figure which has the best info. Birnbaums is $2.00 cheaper but has less pages.
I would go with the Unofficial Guide. Birnbaums is Disney's Official Guide and is a bit too syrupy sweet, if you know what I mean! The Unofficail Guide covers a bit more and covers everything more in depth than the other, too. The online bookstores often have good prices and no shipping. HTH!
We got the Birnbaums because the kids like to look at the pictures and read a little of it. It also has nice maps. The kids would not have even picked up the Unofficial Guide, which can be good, because no one has your book when you want it!
The only one our library had was the Unofficial one so I used it this summer then bought the 2009 version myself. It is humorous to read and has info on hotels and food. I like it, but I have never seen the other one so I can't compare.