I agree with Ian. You always need to be sure of the quality of teachers, what their background is and what their specialties are. The experience, training and education will set the tone the entire class. You might know your teacher can ace the GMAT - - but can they teach? While I'm a natural educator, when I worked at a big company, I was thrown into a grad-level test prep course with only SAT training. I also had yet not earned my MA in education. So, I was preparing before each class and learning right in front of my students. Because I learned material for the GRE, it wasn't a huge problem, but now, 16 years later, as a test prep expert and director of a small company, I would never throw someone in the lions den like that - - there is simply no comparison with what my students get now - - so find out who is teaching the class, and ask if any of the master teachers teach the courses at the bigger companies. Sometimes everyone is a master tutor, which is also a great thing.
Keep in mind, also, that the larger companies have a more one-size-fits-all method, whereas smaller, more intimate companies are more likely to be 'boutiques' and will customize their programs to the individual, small group or class. On the other hand, a smaller company that offers a course, might need to lump high and low scorers together. This is important to find out and if they do this, you'll need to judge for yourself if this would work for you.
I think another important aspect to think about, is to address how you best learn and study. Would you prefer a larger course to get down the basics then a few private lessons to fine tune your knowledge base? Do you do best studying on your own with some guidance? Are you a visual, kinesthetic, aural, read/write, multi modal learner? Will the course address this?
Verifying the quality of tutors, program and company is important and speaking to friends, colleagues and prior clients are the way to go. Also, you might find that you speak with people who have tried many programs. We often get clients who have gone through 2 or 3 companies. And we're still able to 'fill in the pot holes.'
Since there are reps from some best companies here, it is a great opportunity for you to speak to people who are actively at the frontline.
Best,
