A while back there was a long thread on these tractors and it included pictures and some of the specs. If you do a search in the NH forums from about 3 or 4 months ago you will see quite a bit.
Basically the TZ series tractors apear to be sub-compact frame units that would be comparable (presumably better) than the Kubota mini-BX tractors and the Massey GC2300 sub-compact.
The big difference between the TC and the TZ series, IMHO is what the tractors are designed to do.
The TZ being more of a lawn style tractor capable of doing real work but limited by lack of ground clearance, but great at mowing and other similar chores yet capable enough to do work.
The TC being more of a work tractor better suited for some heavier work that is also capable of lawn work as well, but probably not as good for lawn mowing as a TZ.
It really depends on your use of the machine as to which is better suited for your property & needs.