Like the previous posters, I am a Kaplan instructor and also a lead teacher with the primary responsibility in the Chicago area for training MCAT teachers. I've also found what the others have said is true. In addition, I've found that the best people to talk to about a prep course are the people who have taken classes in the area where you want to take classes. The reason for this is that there is variation in the strength of the program in part because of the instructors since every Kaplan center has the same materials.
All Kaplan instructors must take any test for which they teach and score in at least the top ten percentile, with the vast majority in the top 5 percentile. After the score hurdle, your Kaplan teachers should have gone through an audition process to see if they have good presentation skills in addition to being a good test taker. From there, your Kaplan teachers should go through an extensive evaluative training process, from which they could be cut, before they can teach a real class. Your MCAT instructors should be experts in everything that is in the Lesson Books, Review Notes, Topical Tests, etc.; They should know both strategy and content. Of course, that doesn't meant that if you say why is B better than D on #5 in the Kinematic Topical Test they'll be able to answer that question right away. However, they should be able to look at the test and give you a timely answer. As a lead teacher whose primary responsibility is to the students and someone who is not very involved in the business side of Kaplan, I can hold my teachers to these standards. However, other centers do not have a lead teacher and sometimes managers hire teachers more based on need than ability.
If you were in Chicago, I could confidently say that we have the better package than TPR and great instructors who know both content and strategies. At the centers I cover, we don't tolerate poor teaching. I have even pulled a teacher off a class who was not preparing to teach his class as he was instructed to do and did for training, and gave it to somebody else who was able to prepare appropriately and do a better job. Every single one of our MCAT teachers at the two centers I coordinate already attends or has been accepted to medical school. The main benefit of this is a connection to what the students are going through and confidence building; however, I would hire people who decided they did not want to go to medical school as long as they were a good teacher and could inspire confidence in their students. In addition, I only hire and train teachers who can teach the entire MCAT course. I find this gives better overall instruction, continuity and integration of the components of the MCAT than the discipline specific teaching of TPR. However, I was told that the guy who writes TPR's MCAT course lives in Cleveland or Cincinnati and he teaches there, so TPR does a good job there. Consequently, there is some variation in instruction and you should talk to people who have taken prep course at your school or in your area. As has already been stated instructors can make or break the course, so finding out this information is important. There are standards for your teachers, but unfortunately some centers don't have the personnel to ensure that teachers continue to live up to those standards.
Let me know if you have any other questions. Hope this helped.
Tony