JPS-
The only tracked mini-loaders I'm familiar with are the Dingo and Bobcat models. I've seen the Ditch Witch at a trade show once.
For my money (if I had enough to buy one), I'd go with the Bobcat over the Dingo. While I've never actually used an MT50/MT52 for any work, I like the track configuration much better than that of the Ding TX420/TX425. The Dingo has almost NO ground clearance.
Plus, the new MT52's have a sulky attachment that allows your wieght to act (at least partially) as counterbalance. Not to mention any Bobcat attachment (for that matter any newer skidsteer attachment from any maker, I think) will mount on the MT50/52 models too. The Dingo's have a different mount.
I don't know if you know how the machines are rated for lift capacity or not, but I'm sure someone here doesn't know, so I'll tell you.
All machines are rated based on SAE standards. Lift capacity is rated differently for wheeled machines versus tracked machines, though the process is similar.
For both types, the boom is lifted to about 4 feet (not sure how high exactly), and the bucket is slowly loaded. When the machine starts to tip, that is it's tip capacity (duh). Now here's the difference: Rated lifting capacity for wheeled machines is 50% of tip, whereas rated lifting capacity for tracked machines is 35% of tip. So you want to keep this in mind too when you are looking at specs for different machines.
Little long winded, but hope it helps.
Dan