Wednesday was "ruins day." I visited sites in Tulum and Coba and the latter was definitely the stand-out. I arrived as it opened and hired a Mayan guide who'd been working there for 12 years, so he really knew his stuff. Tulum, on the other hand, was very crowded and touristy. It reminded me of going to "see the redwoods" at Muir Woods.
Two photos from Coba - the huge pyramid is the only one in Mexico you're still allowed to climb.