Depends on how much time you looking at. The
Manhattan Prep class in my opinion is the best prep class by far. The normal Manhattan class takes 9 weeks to complete then they recommend an additional 2 - 3 weeks of independant study before the test. Manhattan differs from Kaplan in that it teaches you how to actually solve the problems. Kaplan is more trick based. But Kaplan has its advantages in that you actually get to take tests during the class... something mahanttan prep does not offer. If you are looking for like a week long "crash" course I think Kaplan offers that. But if you are totally new to the GMAT take your time and really learn the different stategies to beat the GMAT this can't be learned in a week, remember that the GMAT is a test of preparedness not smarts. Although smarts does help.