Cancun, 2 adults, 2 young adults, December, where to stay?

Not looking for a really busy, active vacation.  Maybe some sight-seeing, but a lot of lounging in the ocean as well.

Consider staying in Playa del Carmen or Akumal to get away from rowdiness of Cancun and closer to sightseeing in Tulum.

I like the Dreams resorts best for families in Cancun.  Best beach-Dreams Tulum,  but the others are all nice as well. How old is a young adult?

Grand Residences in Puerto Morelos.  Excellent service, good value. 

Anywhere south of Cancun (easily driveable and/or reachable by hired transport) is awesome.  Playa del Carmen is nice with enough of a lively (but increasingly party) scene.  Go further south towards Tulum and that's where things get far more relaxing with nice beaches, not too many crowds and still enough laid-back but great restaurants. 

fiesta americana condesa