The GTN is the black version, and it commands a premium over the chrome GSN -- which is the same camera in all other respects. (I'm sure you know that.) I'd say a GTN is typically more in the $65-$75 range, while you can get a nice GSN for $50 or less. The GT is the earlier version, and I forget how it's different (film speed range is more limited, perhaps?), but it's well worth considering as a less expensive alternative to the GTN.
The electronics seem to be pretty hardy on the cameras, which is surprising given their age (but critical, obviously, since the shutter is electronic). What's more of a problem is finding one that doesn't suffer from the infamous "pad of death" shutter linkage problem, and with a viewfinder that isn't hazy. The first problem makes the camera unusable, and the second makes using it an unpleasant experience, especially in low light. So it's definitely worth asking questions, or checking the camera out yourself, before buying.