I find the Unofficial Guide to have tons more information and useful strategy points. To me, passporter is kind of the Cliff Notes version. It has some pockets in it to hold things (like tickets and maps, I suppose) but I've never felt the need to use such a thing. It also has room to write your itenerary and your reactions to the things you did, but again, I've never felt the need.
In terms of the information presented, I'd guess that the Passporter has maybe 25% of the volume of the Unofficial Guide. Having said that, there's a fair amount of information on Universial Studios and, I think, Sea World, but we've never used that part of the book. If you don't want both, its definitely worth dropping into a book store to take a look. I should think that any decent sized book store should have both.
If you're the kind of person that wants the highlights, Passporter may be what you need. If you want to sit down and immerse yourself in all things Disney, the Unofficial Guide is the way to go.