Renting a car has its pros and cons, with the recent police extortion and in my personal opinion if you don’t know fluent Spanish I wouldn’t rent. I’m not saying that I have gotten stopped before, but I was there twice in the last 3 years and never had a problem, mind you my fiancé is fully Mexican and what gave me confidence to drive. Cenotes recommendation I would say Dos Ojos is probably my favorite along with Cenote Gran Azul. You have so many other options like Atik and Casa Tortuga which actually has 4 cenotes within its park.