There have been many changes since I last visited Southeast Mexico. Among other things, Autobuses de Oriente (ADO) has merged with Ómnibus Cristóbal Colón (OCC) to pretty much monopolize first class bus service in Yucatán. I remember the days when I had to ride the rackety old Unión de Camionéros de Yucatán (UCY) second class buses with their broken seats and cracked windows. There are still a number of second class carriers, but UCY is no more.
Before going any further, allow me to clarify what first class and second class mean. First class buses directly connect larger cities and do not allow passengers to board or alight from a bus between its origin and its destination, unless the city is of a certain size. A bus from Mérida to Mexico City would typically be first class, stopping only in larger cities en route such as Campeche, Ciudad del Carmen, or Coatzacoalcos.
Second class buses connect small towns with larger cities, or with other small towns. When I go from Mérida to Izamal or Uxmal to Campeche, I will have to take a second class bus. The fare will be less per mile, the passengers poorer, and the bus less deluxe. Most importantly, the trip will take longer because passangers can board or exit anywhere they want.
There is also another class of bus usually referred to as combis. These are multi-row vans connecting even smaller cities. Typically, they do not leave until they are full.
Instead of renting a car, I will travel around Yucatán and Campeche states almost entirely by bus. In some cases, I may join a tour organized by a local travel agency, but only to visit some ruins that are harder to get to via public transportation. When I return from Mexico, I will hopefully have some stories about bus travel in the Sureste region, as well as scads of my own photos.