I can only speak for myself but after having three diesels I think I have an idea of what's best for me. Bought a 2006 Dodge quad cab 4x4 3/4 ton stock diesel loaded with low miles, cheap. Make sure the front end is tight. The older 5.9 is easier to work on an has less******installed and gets better mileage. Make sure the engine has good compression and the body has little or no rust. Updated the transmission to a heavy duty towing trans. What a difference. Found a used 65 hp Quadzilla towing chip. Put Bilsteins all around. Michelins underneath.
I now have a great towing machine. If I was to pull a larger 5th Wheel I would get a dually one ton but not necessary with my weight load. I can install a exhaust brake if I wish but not needed yet. A lot cheaper than a new one and runs a lot cheaper.