I've got a GTT and asked myself the same thing for my daily. Its a great car and I love it majorly, its easy to live with/great to drive/fast enough...ok its 'fast' but its never enough/good on fuel but after owning it for ~2yrs I find myself craving a GTR and every time I see one I want one more, and am thinking of making the swap
If I were you i'd go for the GTR, only thing I dont like about them is that they are older, but there are some damn fine examples out there that make it easy to forget
Either way though you cant go wrong, both nice cars