all depends on how much money you want to spend.
GTRs are much more expensive than the other cars you listed so I would assume that you can't afford one.
The other three (s13, r32 gtst and z32) all have their merits but they are totally differnt cars. See if you can drive a few!
And I know I won't win any friends saying this but stock r32 gtst(s) are pretty average, so unless you plan on doing a bit of work to it I would go for one of the others.