5th Wheel Towing Vehicle - Pros/Cons
I'm not sure about today's truck, but when I bought mine, the coil springs were only an option for the Ram 2500, all the Ram 3500 came with leaf springs. I guess for heavy-duty applications, leaf springs were still the best. My previous vehicles were 1994 Ford F350 and 1989 Ford camper van and they both had leaf springs so I've never had rear coil springs to compare.
When the Ram 3500k was brand new, the suspension was quite stiff but has worked in over the years. Now I don't notice it with regular driving, also carry about 500 lbs worth of stuff in truck boxes, so that helps. It's very smooth hooked up to the trailer weight.
I only notice now when I go off-road without the trailer on really uneven ground, it can get a little jerky to drive, but heavy diesel trucks aren't that great off-roading anyway.