Why not both? The G is mechanically the same as the Z, so all of the performance parts fit.
I will agree that everything on the Z/G is expensive, even still on a 10 year old chassis. I started with an SR swapped S13, went FWD in a G20t, then the G35. G35 is waaay superior to the s-chassis, in terms of comfort and features, but it's also big, heavy, and expensive. Looks are subjective from person to person, I think they both are great looking cars. I picked up the S14 last year as a project car mainly because I was familiar with it and it's cheap fun. I've spent almost $3K in performance mods on the G, and have about $3K worth of parts for the 240SX (engine swap, etc) and I'll say the $3k goes a lot further, in terms of performance upgrade over stock, on the 240.
Clean S13/S14s are getting harder to find, they're getting old and the drift craze has turned so many of them into missile cars slapped together as cheaply as possible. So far the first year of owning the S14 has been focused on restoration: new rubber seals around the doors, new dash/radio panels, replacing all of the dry rotted bushings, new sunroof, etc. I started the SR swap last month and luckily am working off a front clip, so it's getting retrofitted ABS, complete rear subframe with VLSD and 3.7 gears, new steering wheel, etc. Goal is to have a clean, tastefully modified Kouki for my wife to drive around. I just happen to like them both.
