STI all the way..
STI more practical, you can drive it in the winter, 4 doors more room.. etc
350Z.. Ugly unless you shave off the dumbo sized door handles.. ugly body kits.. ugly mods and Zero practicality..
if it was a fair comparison it would be between Infinity G35 and STI
I've seen tons of G35's with Winter Tires booting to work in the winter
... 350z Zero
but hey thats my opinion

cheers
Martin