Depending on your skill level some books are better than others.
Marv and Dave's books aer wonderful both in direction and in the teaching of anatomy and expression. These two books are essential to caricature and expression and once purchased you will want to keep them as a reference for future carvings/designs. Given this these books have the most value in my collection.
The Blockheads book is wonderful in that you just start with a basic design and you can transform it to almost any character. This book is worth it's money in just the number of carvings it can produce albeit from a similar blank. Once you have the basics down away you go.
I used Tom Wolfe's books to get started as a lot of carvers have. I probably boought more of his books than I should since once you have the basics of carving an animal or human using his techniques you have the basic skills necessary to branch out on your own. His books do cover a variety of subjects though and I'm sure you could find one that appeals to you. These books are a good carving value in that you get your moneys worth in carving but might not want to keep beyond that as they have no reference value.
As far as Desiree's book goes, I personally have not found value as I tend to lean towards knives and less towards my foredom. So I cannot evaluate this book fairly.
To be honest I have found lately the WCI (Wood Carving Illustrated) magazine to be a wonderful read and reference, which I think all people on the board would agree, and have become collectable just for their usefullness (just ask HiHo). The issues of this magazine take up roughly 15% of my bookspace and that is only because I do not own all of the issues!
Just my 2 cents.
Tony