It really depends on what best fits your studying style. I used Kaplan and found it to be okay. I had average scores, in that it was enough to get into a Master's program, but not a PhD program.
I am currently studying to retake the test. I have a 6-month study plan and have been using magoosh.com. I am finding it much more helpful than the books. There are lessons, timed quizzes, and practice tests. It is also interactive. If you get a question wrong, it will explain the answer. You can also compare your pace to the average pace to answer a question.