I tried a Kubota ZTR on my very bumpy property, after being told I could cut my mowing time in half compared to my old
B7100 with 60" MMM. ZTRs list very high mowing speeds. If I hadn't had my seat belt fastened, I would have been thrown off the one I tried, a number of times. My
B7100 has a full suspension seat and, with its much larger tires, goes over ruts with no problem. The ZTR dropped into the valleys and slammed out of them. As long as my 30 year old tractor keeps mowing, I think I'll stick with it.
For cut, I would go with Scag or Exmark. For ride, I would go with Ferris or the try the new Scag Cheetah, with its fully suspended operators section. For engines, of course the Kubotas or the Cat diesels. However, be aware that the big diesels weigh a lot and can be a problem when the ground is not dry.