Diesel is better quality, always 45 Cetan by law. Way less smoke and better economy for my truck. At least at the Baja all was ULSD. And i was told that all Mexico did the transition to it now.
Biggest change in Fuel business in Mexico is that there are now multiple brands available like BP, Chevron and others, its not all PEMEX anymore like in the past. I think that helped a lot for us customers, especially the new brands look for customers satisfaction and do not even try to cheat.
DEF, yes to but not available everywhere, i saw it in Autozone, this chain store is in every bigger city.