The best way to get around in Mexico is usually by bus. The first-class buses there are outstanding: very punctual, lots of buses on every route, very clean and quiet, and very affordable. The ejecutivo class buses are the "best of the best" with enormous first-class seating, incredible leg room, and services like drinks and snacks available. My favorite of the ejecutivo buses is ETN. They're mostly in central Mexico, but they run long-distance routes to pretty much any major city you want to visit.