I don't have a lot of experience, but I did stay at the hotel Plaza las Glorias in Cozumel. The hotel is very close to downtown and the cruise ships. The dive shop (Aqua Safari) has fast boats with few divers each that go out early. You might ask to do the Columbia reef and for your second dive, check out the ship that was sunk nearby. For me, a relatively inexperienced diver, those were really fun dives. Oh yeah, the Paradise reef was a shallow dive (around 45 ft.) but the experienced divers with me remarked that the fish there were comparatively much larger than they had seen before. If you have just a little time left before going back to the ship, you can dive off shore from the hotel just a few feet from the dive shop.