In my preparation for the new, revised GRE, I have used this book from Princeton Review, Kaplan's New GRE prep book, Barron's essential vocabulary, "30 Days to a More Powerful Vocabulary" by Funk and Lewis, and various dictionaries, Latin dictionaries, and various sources for word roots.
Essentially, it is impossible to find a single book that can fully prepare you for the GRE, but I find that Princeton Review's New GRE prep book has been the most helpful. Here's why:
1.) Above all, Princeton is the most readable. It is written in a very conversational style which makes it easy to read quickly and still understand. This helps emotionally to calm nerves and boost confidence. By comparison, Kaplan is very dry and slow. I worked through Princeton and Kaplan simultaneously, doing math in one and verbal in the other and then switching, and I always found my Princeton sessions to be much more pleasant and rewarding.
2.) Princeton explains processes much more clearly than Kaplan, and Princeton has more structured ways of teaching. The book stresses learning methods rather than memorizing examples. It identifies the different question types and plays out step-by-step processes better than Kaplan does, in my opinion.
3.) Princeton has high usability. The organization is set-up clearly and concisely, so that information may be easily found and understood. The paragraphs are short (and therefore not domineering), and boxes on the side highlight major points of the text in bulleted or list format. The only gripe I have with the organization is that the answers are found in the back and not directly following the section, but this also prevents cheating.
4.) When comparing verbal and math sections, I found Princeton much more helpful with the verbal, reading, and essay aspects. I felt both books did a sufficient job on the math sections but that Princeton did a far-superior job with its verbal and essays sections. This is perhaps because of the warmer, informal style in which it is written that makes confusing, oft-debatable analytical or critical thinking questions much more understandable. Overall, the reader can just see Princeton's logic better.
5.) Although this would not seem like a big deal, Princeton is physically more appealing. It is lighter than Kaplan and requires less effort to keep the book open on its own. It also has a serif font, which humans read better than sans-serif (which Kaplan uses).
Despite its upsides, it does have some downsides. Therefore, I cannot give the book a five-star review. Here are the cons:
1.) Various typos are found in the book, but some are also found in Kaplan. If you ever question an answer, it is wise to go online and look up any revisions that people have posted.
2.) Kaplan has more practice problems than Princeton. Princeton has short practice sets of approximately 5-10 questions after every several pages, but no cumulative sets aside from the 2 full-length practice tests. By comparison, Kaplan has two cumulative math sets of 60 questions each at the end of the math section. But again, it is more important to understand how to do a problem than to just memorize a ton of practice sets, but practice is always a good thing. Princeton has separate practice books which I did not waste my money on.
I did not purchase the disc with the Princeton Review book, as many commented that it was worthless. I have found the Kaplan disc to be frustrating to navigate, and it does nothing different than what Powerprep II software can give you for free on the ETS website.
I recommend Princeton Review above all, but I also recommend consulting many different books, including reading philosophical or scientific literature in preparation for the essays. My suggestions: works by Bertrand Russell, Stephen Jay Gould, E.O. Wilson, David Hume, and Carl Sagan. Flashcards are also good for vocabulary, but it is always more helpful (and frugal) to make the flashcards yourself.