300zx has my vote, you can pick up really good NA's for around 10, with out really anywork needed. If your planing on getting one, get it now not in 5months, apparently legislation has changed with improting 15yo cars so ive herd they recon the zx's will go back up in price.
I feel the zx turns more heads then a stock r32, (thats jsut my oppinion) my mate owned one for a few months and there not as common as skylines, so when you see one with the roof of you tend to get alot of looks.
As for visibility, i drove the zx and its pritty piss poor for a young driver, my first skyline i drove was the r33 gtst, and i felt like i was sitting in a high chair compared to the zx, so as for visability the skyline has my vote. When leanring a new car, if you get a z32 and it has a front bar, on it i dought it'll last, its really hard to tell where the front of the car is on the z32, alot of guess work, wich is hard when your learning a new car.
As for parts i don't agree with ppls comments, the aus300zx forum is a graet source for offen perfect second hand parts. First of all the NA engine is bullet proof, but if parts are needed ppl are forever writing these cars of, as my friend did, now we have been stripping her down and selling part of it, and i tell ya you can pick up alot of parts very very cheep. Thats also how i can comment on the z32 engine bay, freom stippring it all over i can tell you working on it sucks LOL you need to be 12years old with small hands to get into half the places.
As a young P plater with the new regulations (thanks god i got it a few months before) you should hold onto it for the 3 years or w/e it is, and then sell it and buy a turbo'd skyline. Honstly i feel a stock NA Z32 would out run a stock NA r32 no questions asked, others will argue, but after racing around in one, you will see how well the z's handle the corners, i thinks its becuase there really wide low cars, im not sure.
Anyway thats my 2cents worth, but i would go the 300zx
I was in your boat about 1 week ago tossing upbetween a skyline or zx, and i ended up with the r33 gtst and coudlnt' be happy, but if i was on the new regulations with non turbo requirments i would probably has chosen the z32.