between the two i'd pick the vr4, simply because of awd and the fact that it has a backseat.
The 300ZX has a back seat too. Well, more specifically, some 300ZX's have a back seat. The ZX was available both as a strict 2-seater and as a 2+2. The 2+2 ZX's have a longer wheelbase than the strict 2-seaters.
I'd go with the Mustang personally, but only if you're talking about a Fox-platform 'Stang with the 302 cid V8 (aka the 5.0). I don't care much for the new 4.6 litre.
Between the 3000GT and the 300ZX, I'd go with the ZX because the GT has too many little electronic doo-dads and I've had quite enough of dealing with electrical problems in cars. Plus, the ZX is "purer". I mean it's more simplified. A good sports car, IMO, should not be complex.
ZV