Renting a car is the best way to move around here. The best buses might do is get you close to your destination; from the highway, it can be a hot walk to the coast. Another option is to hire a car and driver.
In Case of Emergency -- The Riviera Maya, south of Puerto Aventuras, is susceptible to power failures that can last for hours. Gas pumps and cash machines shut down when this happens, and once the power returns, they attract long lines. It's a good idea to keep a reserve of gas and cash.