I have the Tigweld 160 SX and I could not be happier. If I understand it correctly the only difference is maximum amps, the 200SX is able to go with higher amps.
I have never TIG welded before getting the machine, but it was an easy learn machine. My welds are no where near the quality of some of the pros on this site, but all of my neighbors have been impressed with my welds.
It does not have pulse, which would be an advantage, but Longevity does have pulse machines. I just could not justify the increased cost for the little bit of repair work I do around the house.