I've got three certs through sport chalet (2 different locations). The OW was great. The AOW was horrible. Nitrox was a joke but a very young instructor. However, since I already had a mentor teach me much more, I just needed the official cert.
OW and AOW was a classic example of how the instructor matters. What's more, what the instructor is good at matters. My OW was private instruction and the instructor did a great job and I felt very comfortable when I was done. I started AOW with the same guy. With a very small group, his ability to monitor several was very disappointing. I finished AOW with a different instructor.
Read the linked thread above and ask all the right questions. DO NOT BE AFRAID TO ASK FOR A DIFFERENT INSTRUCTOR IF YOU AREN'T COMFORTABLE WITH THE FIRST ONE. Of course, if you go through 2 or 3 instructors, might not be the instructor.