I’ve stayed at El Cozumeleno 3 times myself, very nice resort. Good All Inclusive deals too. They have a dive shop on site that I was pleased with. I recommend the Paradise reef location for sure as one of your dives. Also try the Sunset Catamaran Cruise they offer at the dive shop if you get a chance, its a good deal. My last stay there was one week before Thanksgiving, there was a little problem with some beach erosion at the time which wasn’t happening on my previous Summer trips. Perhaps its a seasonal issue. Other than that everything was great and I can’t wait to go back!