Cancun - Advice on specific excursions (over Christmas week; from Hilton Mar Caribe hotel)

[Anonymous]

hi - we are visiting Cancun in late December for a week, and I am trying to figure out some excursions. I haven't been to Cancun before - do people usually book excursions with something like Viator or through the hotel itself once you get there? Since we haven't been before, I am thinking we will go to Isla Mujeres and Chichen Itza, but I would appreciate advice on where to go and specific tour operators if you have recommendations (or who to avoid) of reputable tour companies. Thank you.