I have been to both Cozumel and the Caymans. My last trip to the Caymans i stayed on Cayman Brac. If you like big fish encounters, try the Caymans!! If you prefer really beautiful drift dives, where there is hardly no swimming required and small critters, then Cozumel. If i had to pick, it would be the Caymans!!! I also believe that there are less divers in the Caymans.