Honestly you are dealing with a particularly small car market. As most have pointed out its more a matter of picking up a car in good condition than anything else. Both of these cars are not new - a r32 GTR is atleast 10 years old - that means it will require a certain amount of maintenance. You also want a particularly old car in good condition whilst being stock. Anyway, the point is its your probably can't afford to go looking for a particular car ie a black, r32 GTR in great condition with <150,000kms (dont believe the odometer either) as it really limits your option.
BUT on the other hand both these cars are GREAT cars - the r33 is slightly heavier (50-60 kgs), definitley roomier, probably better condition & updated HICAS & breaks BUT an r32 is lighter & has more of a race-car feel.
But the trouble with imports is a 10 year old engine probably won't be in as good a nick as a 6 year old engine so it kinda evens out performance a bit - just depends on EACH car (include mods to as they can be expensive $$$ but also can be a sign the car may have been thrashed in Oz or Japan.
So the main thing to take out of this is just judge each car on its merits as you test drive it - but definitely test drive as many as you can particularly r32 & r33 in both GTS-T & GTR also say a HSV VS commodore to give some perspective.