I think the most important step in looking for a course is assessing your needs by taking a practice test. You can get two free from GMAC when you download their free GMATPrep software. From there, you can figure out how close you are to your goal score and what your weaknesses are. For example, if you are reaching your goal score in verbal and just need help with quant, you may want to get a on demand course that allows you just to purchase the quant section. If your weaknesses are more evenly distributed and you thrive in a classroom setting, you may want to get a whole classroom course.
Hope this helps!