I think it comes down to this.
If you had UNDER $40k to spend on an R33, you'd probably buy a GTS-t and spend whatever remains of your budget modifying it.
If you had EXACTLY $40k to spend on an R33, (the price of mid-level R33 GTRs these days), and not one more cent, you'd probably buy a GTS-t and modify it.
If you had MORE than $40k to spend on an R33, you'd probably buy a GTR and modify it.
Bottom line: I don't know of any GTRs that are left standard. If you can afford a GTR, you can usually afford to modify it. And we all know how well GTRs respond to just a few simple breathing and boost mods.
But then you move into whether you want to modify it at all? Perhaps you like your cars stock? or just with a few mods like intake/exhaust/boost? In which case if you had $40k exactly you'd buy the GTR.
There are a few exceptions like Buster and B-Man who think they prefer the GTS-t over GTR at any price, but they have never owned a GTR so they can't really say for certain