Hmm - asking that on a skyline forum can be a bit biased - but look, there are heaps of nice jap cars out there, so test drive your potentials:
drifting - silvias, 180s, rx7 etc
circuit - skylines, supras, silvias, 180s, rx7 etc
(these are just my options if i was to get one though)
Go for one that you feel is right for you in terms of power, handling, looks. Keep in mind that if you want to do mods, then which is the easiest to mod up to get the most performance gain, which is the cheapest to mod up to get that performance gain. Check out Munna1's website on tuning, thats very helpful and gives a rough indication of the power increases through each mod - and also gives u a bit of info on the skyline
Look at insurance as well - cos once u get those mods on, it might go higher.
The only bad thing about the skyline (or any hi performance cars) is that it doesnt like being on the roads - it much rather be on a track. 184kws stock is low compared to the HSVs and stuff, but even then the rush of the turbo is just so unreal, that before you know it your over the speed limit - hence why its more at home on the track.
You will be looking at around $16,000+ for an s2 r33 - that bone stock (unless someone is desperate to get rid of their car) - but for a modified one, id say around 22grand?
I was initially looking at supras - and test drove a couple of nice ones, but the turbo in the 'line made a lot of difference. In the end it came down to looks vs power - so I got the 'line cos it looked great (with just a very very mild body kit and after market rims) and it had better performance than the Supra SZ. If I was to go for the supra, I would have gone to the twin turbo, that was another 10 grand or so (which meant, i may as well consider the gtr). But in the end, I made the right choice with the r33, and havent really looked back since.