Agua Azul !!! 500 falls from III-VI in 3 miles of multi channeled river, and Palenque is a nice town with one of the best archeological sites in Mexico,other rivers in the area. It's more difficult logistically,but worth it,nearest airports Villahermosa or Tuxtla Guitterrez probably a hassle with boats.
Too bad about the problems in Oaxaca,one of the nicest cities in Mexico.If you are on the coast for Copalita and Zimatan,Puerto Escondido is not far,my favorite beach town with world class surf.
Veracruz best bet for outfitters ,boat rentals ,,etc.,good creekin' and river running.Veracruz and Jalapa= fun cities ,Jalcomulco anbd Tlapocoyan= boaters hubs.