if you're talking about R32's there's
RWD models:
GXi - 1.8L CA18i engine poverty model (think of it as a 1.8l version of the cefiro sold in m'sia)
GXE - not that much better, non turbo, single overhead cam RB20E engine
GTS - non turbo 2.0L DOHC RB20DE engine, not bad for a daily driver (mine started its life as one). You can get a GTS Type S, which is a GTS with extras bundled as a package (like alloy wheels, bodykit, cd stacker etc).
GTSt -single turbo 2.0L DOHC RB20DET engine. Nice car, not bad for drifting, fun to drive.
GTS25 - non turbo 2.5L DOHC RB25DE engine, uses a non VVT RB25DE engine, so its like a GTS, just with a bigger engine, no significant improvement. Rare as it only sold for the few last months of production of the R32, alongside the R33.
All available in 2 door and 4 door variants
then there were the AWD versions:
GTS4 - single turbo 2.0L DOHC RB20DET engine. Pretty boring car to drive, the ATESSA isn't as good as the GTR, and due to its power distribution is a bit dull to drive.
GTR - twin turbo 2.6L DOHC RB26DETT engine. Its a GTR, that's all that needs to be said.
R33 and R34 are similar, but names are different. I won't go into detail about them because you seem interested in R32's only. R33 GTS = RB20E model, R33 GTS25 = RB25DE model, R33 GTSt = 2.5L single turbo RB25DET model, R33 GTS4 = AWD 2.5L non turbo model. R34 GT = n/a, GT-t = single turbo, GT-Four = AWD model.