Amazingly the nicest busses I have been on are in Mexico (Tampico/Monterrey). They have huge comfortable brand new Merc busses available, with fully reclining seats. No wifi yet but some busses have plane-style entertainment systems.

The contrast between those and Grehound McAllen-Houston was amazing, more Spanish was required on the US side of the border, and it was hard to immagine the bus was road legal.