16s or wide 15s. 8" wide is a good width all round.. (if you have power steering)

for completely flush with guards, you'd want et 25 at the front (with stock gti plastic arches) and et 15 on the rear.

with g60 arches lower the et by 5-10 depending on how phat you want your rears. rayray's wheels are a good example of this..

if you want a stock-ish look 15x7 et 25 all round is a good choice