Full disclosure: I'm not currently a 350/3500 owner...I was though.
We picked the 5th wheel trailer 1st. Because it's something I care about, I evaluated the trucks that (with GVWR and GCVWR) would have the capacity to pull/carry the 5th wheel when loaded. At the time (for whatever reason) that brought it into the F350 or 3500 Ram.
The F350 had the full crewcab and full 8' bed that we wanted. Ram (at the time) didn't have that combination...additionally, I simply didn't like the layout of the Ram front seat. Purchased the F350 for our 39', 16k GVWR 5th wheel.
Worked great until sold a few years ago. The current "Tow Vehicle" is an F550. We picked that because: a) only manufacturer that made that class vehicle in what "looks like" a pickup model; b) the Ford cab layout still felt more comfortable than the Chevrolet layout (even though the C5500 is "bigger"); and; c) the F550 works better for the snowplowing (winter) and equipment hauling ( summer work with pintle-hook trailer, not 5th Wheel) than either the 350/3500 or 450/4500 class trucks.