I did Tulum on my first visit and Chankanaab on the next. I prefer Chankanaab. Tulum was an unforgettable experience. But, it takes all day to ferry to the mainland, walk through town, board busses to Tulum with a stop at a fake jewelry factory and maybe an hour and a half at the park. The tour is very structured. OTOH, you hop a taxi to Chankanaab and do what you please when you please. Plenty of time left for sightseeing in town or Carlos n Charlie's. Also, at the time Tulum was $90 pp and Chankanaab $12 pp plus taxi.