That question is incredibly vague..

Depends what model STi, what model GTR, mods, and situation....you want the winner for best fuel economy, drag racing, track, interior comfort, reliability, parts availability, modification potential or what??

In general, stock vs stock, GTR will outrun STi in a straight line, every time...according to a magazine I have here, R32 and R34 GTRs run 13.0 standard, with the R33 running 13.1 standard.

Although an STi has incredible tuning potential, the GTR can run deep into the 12s with very few mods.

Everything else is comparable IMHO.