Simple answer
Gasoline
Ultra low sulfur Diesel is only sold in Baja, some cities along the border and no where else in the rest of Mexico, the urea treatment additives for the catalytic to work are sold again only in the border areas.
Stay with gasoline, gas motorcycle, gas truck, gas generator I will recommend the small Honda unit, depending on the load that you need, if you go off the beaten path gasoline is easier to find not so much Diesel and many times it is contaminated with water.  
Keep in mind that there are more Ford dealers than Chevrolet and Dodge in Mexico.
navegator