I try to dive the cenotes everytime we head to Cozumel at least once, usually twice a year. I have only dove with Cenote Experience and see no reason to dive with anyone else as long as they are available. Martin is an amazing guide and one of the best divers I have ever seen. More importantly, we have never had a surprise or a no show, or even had them show up late. Everything runs exactly as planned. The cost is slightly higher than a normal reef dive ($125?) but well worth it in my mind. I usually ferry over from Cozumel, Martin meets me at the ferry, and we drive to the shop for tanks and paperwork then off to the cenotes for the day. The water is a little cooler but I was fine in a GOOD 3mm, low flow wetsuit and a hood.
I did 3 cenotes the first time in a day and I was pretty tired by the time we got back to Cozumel. It was a long, but fun day. 2 cenotes is about right for me.
Good luck, safe travels,
Jay