Before I retired I worked for a large truck equipment dealer. I would say 85% of the work trucks (F-250 and bigger) were Ford. The other 15% was Chevrolet. No Dodge trucks, we couldn't install work bodies on them because the frame was too weak. That was 6 years ago so I don't know what is the most popular now but I would put my money on Ford.
2014 Palomino Puma 25RS
2011 F-150 Super Crew XLT
Days camped in 2014 - 23
Camped 2015 - 47
Camped 2016 - 51 done - 6 more planned so far