Cancun resorts are about 5-20 minutes from the airport. They tend to have very active resort environments and wide white-sand beaches. The Cancun hotel zone offers the most amount of activities, tours, shopping and nightlife.
Riviera Maya resorts are about 45-90 minutes away from the airport. The beaches are more narrow and stretch for miles. Riviera Maya tends to be on the quieter side, since everything is a little more spaced out.