Puffer the cenotes are ok for a newer diver as long as you go with an experienced guide. I would recommend Cenote Dos Ojos. Its near Riviera Maya. The first few hundred yards are very open and offer almost out of this world sights. They have lines run, there is an amazing halocline. I have been cave diving in that region once or twice a year for the last 10 years or so. Its worth the $$ for safety's sake to go with an experienced pro. I would never cave dive without redundant equipment, especially an extra mask, lights, air, etc... A good guide will have all this and more. I prefer rebreather vs scuba for caving. You will want to be able to "frog kick" and practice bouyancy control before going into any cave, as once you kick up dust in a cave it gets hard to see and takes forever to clear up. Not trying to scare you, but it does take a little more thought than open ocean diving since you must always know how to get back to the surface. The Island of Cozumel has some awesome caves but most are less accessable and not as open as Dos Ojos is why i would recommend that as a great "starter" cave.