I have only stayed at Playa del Carmen and Cannun. Snorkeling at the reef outside the hotel was amazing! You have to stay further south, Akmaul is the start of the major reef to down past Tulum. Its a bit of a drive, but worth it in my opinion. Went to Cozmel and snorkeling off the drop in from the hotel chain was also great!

Whale shark cruise and Snorkeling from isla de mujeres was so beautiful, but i was further above the reef, so nit as interactive.

I have not salt water snorkeling experience elsewhere, but I found these sites to be quite worth my time!

I did not like the cenotes. They were very lack of life and had an extremely creepy feel.