MGMAT -- Excellent (but you can self prep)

Part of my debrief includes my feelings on MGMAT:
http://gmatclub.com/forum/second-try-is-the-charm-710-48-q-38-v-79956.html

In a nut shell, learning as a 20+ something is much more difficult than learning as a 8-20 year old. The older you get, the more set you become in your ways (yes all ways), so if you have subconscious tendencies that are wrong educationally (math, grammar, etc.) it will be VERY difficult to get over those obstacles on your own. MGMAT puts a lot of emphasis to help you understand the "why" aspect of getting answers incorrectly. Obviously, a 1:1 is much more helpful, but the program does cater to this. The instructors are top notch, the material is excellent, but you as a student must invest the time to utilize these resources.

The flip side is self prep is possible, but you really need to invest the time to identify these tendencies and overcome them (the importance of the error log). No matter what you decide, the GMAT is a test that can be overcome, but you must invest in what your needs are (there isn't a one size fits all).

The class is well worth the money.