I'm looking for a used CTL tracked skid steer for farm work. Clean up, some dirt work, woods clean out, etc. The question I have is undercarriage and its real effect in an offroad/farm/woods environment. I've rented several skid steers from local Boyd Cat facility for farm work, and my biggest complaint on the farm has always been the roughness of ride going over/through any sort of ground change. I will use it on uneven (not really rough) farm ground and in woods. What I found on the fixed undercarriage machines I used, was ever little bump/stick/pothole ended up rocking the entire machine. I felt like I was constantly climbing then falling over the terrain. I have never had the opportunity to try the MTL or ASV bogey undercarriage, but it seems like it would be the best for what I need on the farm, as it would allow me to go over bumps, sticks, etc without requiring the 'climb and fall' for everything. But I don't know. I know that undercarriage has fallen out of favor because it didn't hold up well with gravel and construction requirements. But I wouldn't have that sort of need on my farm, as a general rule.
Yea the ASV/MTL undercarriage is not highly regarded for the reasons you mentioned. I think everyone for the most part just deals with the effects of rough terrain on a CTL. Having ride control available helps with some of that. Bobcat has had an option for a leaf spring suspension on some models for a while, you might find one that works for you. Case/NH, Deere offer a suspension option but that is a pretty new option, probably wont find one used yet. Buying a used MTL or ASV machine would be your most likely option, just be careful you find one that isn't already wore out. They are expensive to replace as you can imagine. You can't match the ride quality with anything else, but it comes at price.
By your own admission, your ground is going to be a challenge for any machine. I would not recommend the ASV style on ground like that, you will be up against a maintenance nightmare. The Bobcat roller suspension is ok, but those spring packs are $450 per stack, two per roller. You can sometimes take them apart and build one or two out of 4 or 6, but that is time consuming. My advice as a contractor? Just get a solid frame and try and take it easy.
All above is good advise. I have had several skidsteer mechanics tell me that most any skidsteer is ready for costly repairs when is reaches 3000 hrs. They all suggested buying something used, with under 2000 hours if my budget would allow. I can not tell you if this is fact or not, but these mechanics were at several different brand dealers. So, I always stayed with less than 2000 hrs, and seemed to have good service out of them.
I have both a wheeled (case 1845c) and tracked (Kubota SVL65-2) skid steer I use in both my construction business and on my beef cattle farm. Overall I would say the ride is better on the CTL vs the wheeled unit, but the CTL tears up the ground worse when turning. A good seat goes a long way, (air ride is best) and a longer track on the ground also helps. Try some different models, the length on of track on the ground, balance of the machine, seating position, etc all make for different ride/operation characteristics. I've driven some CTLs that ever rock, hole, bump just goes straight up your spine and some that are much more pleasant to operate. Lastly, part of it is just experience running track machines. I ran a dozer for quite some time before buying my CTL and a lot of it translates over. You'll learn quickly what type of terrain, ridge, rut etc will toss the machine around and learn to slow down when crossing them.
I can't remember which models but some Cat's have ASV undercarriage. Why don't you rent a ASV and try it before you decide. If you do decide to buy a used ASV, I would closely inspect it first.
The Cat track machines with a 7 at the end of the model number are ASV suspended undercarriage (like 257). The CTL undercarriages end in 9 (259). I agree with Shimmy, I personally wouldn't go the way of the ASV undercarriage, but as long as your aware of the downsides you can make your own decision. Getting a large frame machine, I think makes for a better ride than does a medium frame CTL. As I mentioned before, having ride control really takes a lot of the punishment out of the ride. If you go ASV, you will likely love the ride, right up until you have to tear it apart and replace it and then you will ask if it was really worth it.