Diesels from any of the three manufacturers from 2011 and on are going to be above average in reliability. They are also going to have stronger frames, except for the Ford trucks. GM beefed up its frames starting in 2011 and Ram did the same starting in 2013 for the 1-tons and in 2014 for 3/4 ton trucks as well.
80% of the 5th wheel travel trailers being towed on the highways are pulled with SRW trucks. Stock tires are fine with a 2500 class truck for 5th wheels up to 14,000 lbs. in weight. Above that a DRW or 19.5 tires are needed.
Not widely known by the general public but Ram sells more 1-ton trucks than Ford and GM/Chevy combined. Probably a good reason for that to be happening year after year. I like the GM trucks with their independent front suspension but my second choice would definitely be a Ram 3500.
With Ford the F-350 and F-450 pickups are virtually identical except that the F-450 pickup has lower gears and the 19.5 wheels and a smaller turning radius. Payload is actually less for the F-450 pickup than for the F-350. You have to get the F-450 chassis cab version to get a higher payload rating.
I would also compare both the largest stock fuel tank provided with the models you are considering as well as the availability of replacement tanks for the OEM one, like the Titan 60+ gallon tanks.