I visited Chichen Itza ~25 years ago, when you could still climb El Castillo, and remembered I was awed by the architecture, especially the feathered serpents on the pyramid, and the many columns in the hall. Definitely worth a trip.
Coba was interesting (about 5 years ago) and they did allow climbing the pyramid, but I believe COVID has stopped that for now (social distancing issues). Coba is not as well-preserved or reconstituted, so some of the architecture looks worn/rough in comparison, but it has a "lost in the jungle" feeling to it.
Tulum is mainly about the location - beautiful Caribbean right below the ocean. The architecture is small and not as impressive. When I went ~20 years ago, we could swim in the ocean right there, that was nice.
I hear great things about Uxmal, havent been. Went to Merida about 20 years ago, a beautiful city, colonial architecture, Yucatecan food, great shopping and would second Merida/Uxmal as a worthy and easy side trip from diving.
This would be a very far land trip, but I did it in my energetic youth 20 years ago - Palenque, in Chiapas was really impressive architecture, purely Mayan, and interesting to compare to Chichen Itza, with its central Mexican influences. LOOONG bus ride from Merida (although you could break it up by visiting Campeche, which I hear is a pretty colonial city) - by bus, my itinerary was Mex DF -> Oaxaca -> San Cristobal de Las Casas -> Palenque -> Merida -> Playa del Carmen, ohh, to be young and dumb again!!)