My husband and I just got back from Cancun and we STRONGLY recommend Mayan Aqua Dive. I dove with several of the instructors/divemasters and they were all wonderful (Karl, Isidro, Ulises). I've heard some horror stories about some of the larger dive companies LOSING divers, boats leaving without divers, etc., but the guys at MAD were very focused on safety - they keep divers with divemasters at all times, they pay attention to the divers, and help improve their diving. My husband is kind of a nervous diver, and I noticed that the instructors watched him very closely. They dive open water, wrecks, cenotes (sink holes), and they also have trips with SCUBA Mau in Cozumel (but a MAD divemaster accompanies the clients). We both got our advanced open water certification with MAD and they really focused on the skills we needed help with, discussing them on the boat and greatly assisting us in the water. They also made it really convenient for us to dive with them. They had the same taxi driver pick us up and return us to our hotel for no additional charge, and they kept in frequent contact with us to update/confirm dives (e.g. in case of changing weather conditions). In total, I did 9 dives with them, and I wish I had time for more!! I will be returning to Cancun shortly and I will only dive with this group. I hope this helps - have a great trip!