Well based on what is out there and available, for a mechanical driven trans I think the T-20 is hard to beat. My PPT has a unique trans that uses 2 renault clutches on either side with disc brakes and now I finally got it dialed in and figured out how to adjust it, it works pretty good but there is a lot of resistance on hard surfaces that will almost kill the engine due to load. it needs a bigger engine. If you want a more bullet proof trans then get a Bobcat or similar skid steer hydraulic transmission system.. Owning a couple of bobcats, I can tell you that they hold up to abuse far better than any mechanical trans. there is a reason Hydratek and Mudd Ox are using hydraulics... the down side is cost $$ Hydraulics are expensive however you never have a direct mechanical load applied to the gears that you do in a mechanical system. There is always a fluid cushion to absorb sudden shock loads that tear up parts in a mechanical trans. the worst you do if you overload the system is kill the engine. so you just release the pressure and turn the ign key and you are good to go...
2000 Land Tamer with Tracks.