Like most other reviews on here say, the key thing for you will be making sure that you find the instructor / program that would be the most effective in motivating and guiding you through preparing for the GMAT. No instructor is going to take the exam for you, so making sure that you find someone that will get you to want to improve is absolutely key to getting the most out of any program.
Ravi Sreerama was a perfect fit for me - he doesn't sugarcoat his feedback and will happily let any person know if it looks like they are starting to slack off in their preparation for the exam. When I (or anyone else) needed a push to bring my effort up, he was always ready to give one. He did a fantastic job guiding me through how to prepare for the exam and mastering the strategies and topics I needed to know on test day. When I took my first practice test I got a 640 (37Q, 39V), and Ravi helped me significantly improve and get into the 99th percentile with a 770 (50Q 46V).