This was really my decision as well... 2500 gasser or 3500 diesel. The 2500 would have done all I really needed it to do, but, I wanted the diesel. Wife and I would like to upgrade to a fifth wheel at some point. I bought my truck in Feb 2017, we got the travel trailer a year later and that is really the reason my half ton no longer works for us. I didn't want to be in that position again, either settling on our camper because of truck, or, having to do another truck upgrade.
Having said that, the 2500's are capable of much more if one is comfortable ignoring the sticker on the door. Your payload and hitch weight is going to be mostly on the rear axle. The engine delta between the gas vs diesel is up front. There is a lot of debate about what the truck is capable of vs the sticker. The sticker is based on a 10,000lb GVWR. Doesn't matter if it's gas or diesel, for a 3/4 ton, that's what you get. In the 3500, the gassers get a 10,800 GVWR while the diesel gets 11,700. This makes up for the added weight of the engine.
The coil springs are not the reason for the lower rating, ford and GM are also held at that 10k mark. But, one could argue that the artificial limit is the reason Ram switched to coil springs in the first place. If the sticker is going to artificially reduce the truck's capability, then, why not make it the best riding 3/4 ton in the field.
Anyway, I went 3500, I didn't want to play that game of having to convince myself that the truck wasn't over loaded. I don't blame anyone who feels comfortable with it though. I also drove both back to back hoping that the ride in the 3500 would beat me to death and the 2500 would feel like a Cadillac so that I could convince myself to go with the 2500. But, that wasn't my experience. I felt very little difference if any in the ride. Of course, these were 18's and both diesel. My gut feeling is that the diesel will ride better based on the weight, but, I don't have any evidence to substantiate that. I'm hoping the 19 ride is also improved. FWIW, I also didn't feel like they were that much more harsh than my F150. I'm sure when I have it as a daily driver I'll notice the difference, but, in my test drive, neither felt like a huge downgrade in ride.