it depends on your usage, i have modded a few GTR transfers to RWD only see pic. i even have a spare in the shed.
The benefit of using a GTR trans is they are dirt cheap on average i would pay between 500-800 for a complete setup. The gtr box and modded transfer has much better support (4 bearings vs one) on the output shaft so takes abuse like drifting far better, in fact TRUST japan uses a GTR box and modded transfer behind their sr20 D1GP car as it lasts far longer than the GTs-t equivalent. (something to do with the way the load travels up the output shaft).
the downside is the time and effort to make it happen, i built one up for our RB26 powered s13 but found that due to some other issues i was unable to fit it in the tunnel without reworking the custom handbrake setup and so forth. I ended up using a R34 gtt box.
only the R34 is a 6 speed and it wont fit.
R33 gts t and R34 GTT are the same box but the R34 has some nice subtle upgrades ive noticed.