R32's
are a bit shorter than R33's (33's are HUGE!). Having said that, they're still big ol' cars.
Cosmetically there are huge differences, R33 is a very rounded car, and the theme continues into the interior. Got a nice dash style, very modern (reminiscent of mid nineties toyotas too). R32's have a rather dated dash (IMHO - although I love my R32).
R32's are a bit lighter too, and of course, cheaper to buy.
On the GTS front, R33's are all (I think) 2.5l, whereas the vast majority of R32's are 2 litre.
The GTR's of course are both RB26DETT.
I believe also that R32 GTS's can run higher boost on stock than R33 GTS', but you might want a few more opinions on that one, and it is a 500cc bigger lump.
Both got 24valve twin cam trains in em, and six cylinders inline of course (what other engine could there possibly be?).
In terms of handling, probably not much noticeable difference unless you are used to one or the other.
Theory goes that the R32 is the best handler of the lot,and I'm probably going to get shot for saying that, but it wouldn't be the first time.
Personally, I think you'd have to be close to your own personal limit to notice much difference in that respect.