i used to own a 33 gts-t and now S15.
handle heaps better
i have tein HA in my R33 and only kings spring in S15, the s15 handles a lot better than R33, specially on the limit, maybe becoz the S15 has a GTR style LSD. The rear feels like it always want to kick out but doesn't. Even it does, it is easy to control, but the skyline, is a bit dangerous for me
performance
the S15 out perform the skyline with less mod, FMIC, turbo back exhaust, SAFC, 1.1 bar of boost, and high 12's is not hard to achieve
maintance
the car is nearly 200kg lighter, so u go figure the wear. Tyre, brake, clutch everything, being lighter S15 can achieve same perfromance with lower hp, lower hp = less wear.
i also get 525km out of a tank for s15
475km from R33
drive style? i gun the S15 more than R33.
all around feel
skyline is better built, feel more solid, goes smoother. The sr20 rattle a lot and sounds crap.
S15 is not a well built daily car, the looks good and goes well, but not durability.
my S15 is nov 2002, done 27xxxkm, rattle noise from the dash, the power window give up 2 times and there are a bit scratch in the interior
none of this happen in my R33 which i own for 2.5 years and driven 30000km+
i can image thing in S15 start fall apart in a few years time, but not in my 10 years old 33.
R33 is a more mature car
weekend warrior/ second car - S15
daily - R33