JCat,
you would be surprised teh differences in manufacturers of tractors and what they are being used for will also make a difference. Plowing fresh soil is rough work, discing soil for teh first time is rough as well, tractor weights will make a difference. Some have an air ride seat, some just springs and some are solid mount. Then there is teh difference in tire styles, I have hads Kubota's with field tires that were rough as could be but with a turf tire they were a dream to use. Form and Massey Ferguson for some reason are easier on me than others I have ran, i think it's teh weight of the tractor and seats.
Yep I have heard bad things about the short-bar, long-bar tires. They are super rough both in the field and on the road.
The bigger JDs are a longer tractor then most of the other brands plus they have the advantage of having the fuel tanks up front over the front axle. Ballast in the tires helps with the ride because the weight often flattens dirt clods as you run over them instead of going over the top of them.
My old 641 Ford is very good in the comfort dept. even with the old steel pan seat but it is basically mounted to a two foot long spring. There is ballast in the rears for traction and even zipping across a field at road speed it is a nice ride. The only down side to the older 100 series Fords is that the PTO was transmission driven instead of direct to the clutch which is unhandy when baling hay and brush-hogging. If you get a tractor that the PTO is transmission driven make sure that it has what is called an over-running clutch, your fences will thank you for that!
We used to joke at the shop that Case should never be allowed to put the word comfort on it's 930s, they are very short and can be really rough in the fields. Even weighted it's hard to keep the fronts on the ground during a hard pull.
And the weight of the operator has a lot to do with it too. At 225lbs I will be less likely to be tossed around then someone weighing a lot less.