Ford Super duty 350 or Dodge 3500 for towing rv?
Dually is going to give you a better ride when towing. Although I am obviously 100,000% a Ford guy, it really is up to you. Both are very capable trucks. I would research more along the lines of resale value, dependability, and look at the actual quality of the trucks themselves. Drive both. See which one feels better to YOU. Both with pull whatever you want them to.
Get the Ford- I still don't trust Dodge-
It would depend on the year and condition. I would go with the dodge because dodge has the cummins turbo diesel that performs amazingly under any load.
I think ford will give you better value and less concerns with reliability. The more rubber on the road gives a better ride and traction.