For someone who is bad at self discipline, the Manhattan GMAT in-person prep class was essential for me. I tried the Kaplan online classes but had difficulty holding myself accountable. Mark from Seattle Manhattan GMAT was fantastic. The class size was small. Sometimes, there were only 3 students so it almost felt like a private session. I recommend taking the exam 2-3 weeks after the class is over so you don't lose momentum but still have time to do some last minute review. You should also take the exam multiple times to get yourself accustomed to the adaptive format which was the most difficult part of the test for me.