OK - I can give you my recent experience with both makes.
New to Skylines, and the forum.
12mths ago I purchased a 03 STI (with medium mods) - sold it within 3 mths!
Noisy.
Slow, if not on boost.
No torque.
Front torque steer under power.
understeer.
It was like driving a highly strung race car on the street, which needed the crap revved out of it to have any fun. - very annoying.
3 weeks ago I purchased a R32 GTR - stock standard. I love it. I have had plenty of performance cars, currently race a 4cyl Alfa in Historic Touring cars, (I am 45 yrs young), and the GTR is a serious car. It is the real deal when it comes to serious performance cars. I also considered a EVO, but same issues as above with the WRX(to buzzy/rice burner type of thing.
In the end I really wanted a super/muscle car. A make/model with race history, something original and to hang on to long term. I could have spent $40 - $60K on Aussie muscle, but in the end spent $14K!! on a true performance (race) car.
When driven at full tilt, the GTR is a more capable/satisfying/mind blowing/enjoyable experience.
Being from the old school/V8 type back ground, the best way to sum it up is that the GTR is more like a cross over between Aussie muscle with Jap hightech, - if you know what I mean......even my HSV/FPV mates rate it highly - surprise, surprise!!
If you want a "sporty" car - maybe a WRX (but go EVO)
If you want a true supercar (a legend) - go GTR
Thats it, now I'm off for a drive along the coast in my new toy, and then maybe give it a wax, and just stand back and admire. (never felt doing that with the STI)
Steve.