I spent a week diving in Cozumel from the Palace Resort with their onsite shop, Aqua Safari. Overall, they were a good shop; I've give them a B, but not a class A (like valet diving in the Caymans).
They have several boats, all with heads (important to me). The boats have all been around a while, but overall, good shape.
They appear safety conscious; the divemasters are regularly doing a nose count. They spotted my underweighting with new dive gear right away and handed me a spare weight they were toting along. They only dive one way; one group, large or small, with a DM in front and a DM in the rear. A few of the dives were crowded with 15 people in tight quarters all waiting their turn to look at the X.
Dive style varies greatly by DM; some just float along with you until 700 PSI, while others were unbelieveable about searching out cool stuff all the time like seahorses, etc.
If you're a 3 a day guy, this may not be for you. The afternoon dive is always Paradise Reef. There, different dives are still possible, depending on the afternoon DM.