just get what ever looks more appealing to you, they both arent going to go fast, as ive heard i own a gts r33 atm but its still getting fixed and have onyl driven it once, but it felt better than any other car ive driven. personally i think any skyline will feel fast compared to other normal cars, as in its handling department.
one thing you have to consider, which i did, is if you get the r34 gt (non turbo), it will cost at least $10,000 minimum, even more if you want a manual. you have to add at least $2000 on top of that for insurance, as with a $10,000 car i wouldnt just want third party.
but if you got a r33 GTS, you would only have to spend $4000 minimum, plus then you have left over money for handling, stereo, interior mods. plus you can afford to get third party cause its not worth it on a $4000 car.
if that makes sense.
but if you have the money i say get whatever you want, which sounds to me a r34 GT
(make sure its manual) aah