It will mostly depend on what platform you are on. The fords ride the roughest but have the best offroad prowess. The chevy express platform rides much softer but isn't as good off road. The sprinter and transit both ride like a car on road, but are the worst off road of the bunch.
If you are doing a lot of miles, I would get either a transit or sprinter. They get better mileage as well. But they are considerably more expensive because they are much newer than the older fords and chevys (for the most part).
In that case, I would do a ford econoline base with a weldtec designs supsension lift. I would do a 4" kit with custom rear leaf springs. It will run about $5k installed but will ride great on and off road.
Weldtec will ride better but it depends on what you pay for. If you pay for properly tuned springs based on your vehicle weight, either one will ride nice. Iím partial to independent front suspension, which is weldtec, as I think it rises much better. However, Iíve never ridden in a ujoint van.