To be honest with you, it's great to read them but from what I have found is that most of those books contain ALOT of crap, and sometimes information mentioned in those books are contradictory to other seduction gurus.
"Double your Dating" as well as "Attraction is not a choice" are probably the two best books from David Deangelo. I'm pretty sure these were the first two books I chose to read in regards to seduction/picking up women.
All his other material is pretty much usless, particularly the DVD's and tapes - don't waste your time on those!
However, I should warn you that some examples of ****y humour that is shown in the book aren't so great, I would look at some examples from this site and other DJ sites.
I would also recommend you reading "The Game" from Style - a great read for sure! It has some useful tips inside of it, it's pretty long, but I found it to be humorous.
But remember, these books are just to get you started off. I have roughly 30-40 e-books from gurus on my computer, I've read about 10 of them.
Most of the information over-laps and once you learn the concepts illustrated in each of those books, you will learn to develop your own style of picking up women.
For example, reading David D's material helped me learn how to create my own ****y+funny lines - I no longer have to rehearse canned material and I am able to apply the concepts I have learned and think of amazing lines on the spot!
Read those 3 books combined with some posts on this forum and you will be more than fine. Most of the other books I have read contained a lot of "filler" material which completely wasted my time.