ps9a, both the Fairmont Mayakoba and the Ritz Cancun are AAA 5 diamond hotels.
While I'm sure the rooms win at the Banyan Tree over those two, I would bet my life that the service and beach are better at the Ritz, as well as the value. (Rooms at Ritz are impeccably clean and comfortable, with beautiful marble bathrooms but definitely not over the top luxury rooms. The Club level is a must.)
As for overall property, the Fairmont looked very nice, and it is a great value...