I think that it depends on what you want to spend on a GMAT test prep guide? The first book I would buy for sure, is the Official Guide to the GMAT, 11th edition. That is one study guide that you need to have first and foremost. Do you have a plan about how you want to study for the test? You should take a diagnostic test, first before you start to study for the test. That will give you an indication about what your strengths and weakness are in regards to the subject material that is covered on the test. Then, you can make up a study plan based on the results of that diagnostic test.
My personal favorite study guides are put out by Manhattan GMAT. You can look them up by going to manhattangmat. com. I am not really a fan of Kaplan or Princeton Review for my own personal reasons. Barron's and ARCO are not very good, either. There is a whole lot of information about studying and study guides in the "GMAT Resources" area of this website. I would go there and look at what might interest you.
Greg