I spent at week in Cozumel (Sept 26 to Oct 3). I stayed at the Scuba Club Cozumel and had a great time. It was so off season that there was only me and two other couples for most of the week. We just hung out together. It made for a very uncrowded dive boat. For me the diving was some of the best I have every done. The group even did the C-53 wreck; a new experience for me going inside.
I know that Cozumel has been reviewed before but I want to say that the boat crew, dive masters (Ariel in particular) and support staff at Scuba Club were great. Accommodations were good and the food, while not gourmet, was actually pretty good as well. Proximity to town was convenient. I would definitely return there.