If I could only get one, it would be PassPorter. I love the whole format. I always get the deluxe binder one since it can hold all my stuff without stretching out the binding!!! If I want I can rearrange the pages to suit my plans...all the relevant stuff up front, less important in the back. I use the day by day pages in the back just like a travel diary. It's wonderful to go back years later and read about that particular trip.
I do get the UG also though. Yes, it's negative but it does give you a good overview of what's what. I have never used the touring plans.
As far as Birnbaums goes...I bought just one...first trip. It's just too pro-Disney. Now, no one loves Disney more than I do, but let's face it...all is not perfect in the World!! So, what I do is get the Birnbaum's for Kids each trip for my dd. She loves having her own guide.
So, each trip I get PassPorter, UG and the Birnbaums for Kids. Now, do I think I really need it after going so often? Nope, but they sure do give me a nice Disney fix when I need it!!