My husband and kids (ages 13,14, and 22) were in Cozumel over Christmas for a week.
We stayed at Casa Mexicana. We enjoyed the hotel very much especially its location. We walked all over at night time for dinner and shopping. The rooms are decent in size and a nice balcony. We were in rooms 302 and 303 which over looked the ocean. They had a connecting door too. The only downsize was the size of the beds in room 302 which were double not queen sized. We are all tall which made it difficult because they were so small. The breakfast everyday was great and plenty of items to choose from.
We went to Chankanaab for a day, the East side for a day, and Playa Planacar for a day. Playa Planacar was very crowded with cruise ship people which surprised me. It was hard to find seats and it took forever to get a drink. Our best new spot is Mike's Beach Club! It was not crowded and the drinks and food were great. We rented two jet skis for 45 minutes for $110. They let the kids on them for way more than 45 minutes. Everyone there was friendly and very accomodating to us. The bathrooms are very clean and the pool is large and beautiful. I would highly recommend Mike's Beach Club.
My kids and I went scuba diving too. We just got certified this summer in the US. I have to say it was the highlight of the trip for me. I am now addicted! We used Aqua Safari. I hired a DM to stay with us. For the three of us it cost $300 for two dives each and the DM. We had to rent shorties, BC and regulator. I liked Aqua Safari but was not overly impressed. Everyone on the boat changed their own tanks. I don't know if that is normal or not but that concerned me slightly because no one checked to see if they were done correctly and most of the people on the boat were first time divers after being certified. Not sure if I would use them again because of that issue.
We have always stayed at Cozumel Palace so this was our firs non AI experience although we always go out and explore more than most. The island was pretty empty except for the cruisers which surprised me. In the evening I felt like it was us and locals out and about with no tourists. It was kind of sad. I was concerned about Christmas day and Christmas Eve having everything closed, but there were plenty of places open for eats and shopping.
We ate in a bunch of restaurants. I am a non meat eater so I was sick of eating the same thing day after day at the restaruants, and salads were not on many menus. I was curious to see how much "cheaper" it was going to be not staying in an AI. We quickly realized it was not really cheaper. Every dinner cost us at least $90 USD plus tip, lunches were not far off from that. When you add in all of the costs for beach clubs, drinks, car and entertainment, it was very close to Cozumel Palace. I did enjoy it and like to help out the local economy, but all in all we would choose an AI for our family. We have been to the island a bunch of times and will be back in March for spring break. Hope this helps people and will be happy to answer any questions.