You have dove Aruba, Belize, the Bahamas, and Roatan?
I spent a week on a live aboard in the Bahamas totaling over 20 dives and 2 days in Aruba with one scuba dive. In Roatan and Belize, I just snorkeled while the rest of the boat scuba dove (I wasn't certified yet).
But, as I will state again, I am comparing the whole trip, including restaurants, motels, and shops in addition to dive ops. My original statement never took issue with the dive ops. I was only making comparison between my Mexico dive vacation and other dive destinations (whether I scuba dove or snorkeled or didn't dive at all is not the issue) that I have been to and the OVERALL impression I got.
If I were to compare the reefs, I would say that Cozumel is lower on the list, having taken a beating from several recent hurricanes. The last time I was at Roatan and Belize (2004) the reefs I saw were in good conditions and I have not heard anyone saying otherwise. My personal experience with Aruba, Bonaire and the Bahamas (granted only about 75 total dives in those locations - I am by no means an expert) showed the reefs in better shape. Some places had more fish, and others had many but small size fish.
I'm really sorry I apparently have offended some of the regular Cozumel divers. That was not my intent. It was only to state that Cozumel was probably the best place to dive in Mexico, if you are set on diving in Mexico. It is also close to the mainland Cenotes with I really thought were awesome. But the overall friendliness of the locals in restaurants, bars, hotels, and shops didn't seem to be a great as other places. Much of this may be due to the fact that I don't speak Spanish, and the other countries always spoke English to me, even if it wasn't their native language.
I'm hoping it is acceptable to have a different opinion and present those opinions for consideration in this forum. I do think I have taken this off topic, since the OP originally questioned where in Mexico, not if in Mexico. I apologize.