Just wanted to recommend Blue XT SEA diving, especially if you are coming to Cozumel via cruise ship. I contact probably a dozen shops prior to the cruise, and only a minority could accomodate our schedule. I had booked a month in advance with Scuba with Allison, but a couple weeks before the trip, she contacted me to say she had to cancel. She helped me make reservations with Blue XT Sea, and it turned out great! I communicated with Christi over email and she is very friendly and helpful. You can pay the whole thing in advance over paypal, which is nice, because then you don't have to worry about walking around with a wad of cash in your pocket.
I have to admit, I was a bit nervous about the drift dive (after hearing horror stories of people getting lost, etc), but it was totally fine. Our divemaster, Pedro, was awesome at making sure the four of us stayed together, but we still had plenty of freedom to stop and take pictures, etc. He also pointed out some amazing things we wouldn’t have seen on our own – a splendid toadfish (said to be only found in Cozumel) and a very tiny seahorse. The surface interval is at a small beach and they have delicious snacks – papaya, cakes, and juices. The two dive sites we went to were Palancar and Delilah reef. I would highly recommend Blue XT Sea to anyone diving in Cozumel!!