not a CDL but grew up in a construction company - F800 single axle trucks for a lot of equipment hauling. We built power line so a lot of our work was off-road. 4x4 was pretty necessary to get around so all our F250/F350s were 4x4 pulling gooseneck trailers to get the equipment to the job site.
I pull my 5er with a 4x4, mostly because it's what I had, but I use the 4x4 to get to my hunting spots (with the 5er as hunting camp), and a lot of other off-road or snowy, muddy road access.
If I were doing mostly highway towing and didn't already have a truck, I would probably consider a 2x4 strongly.