Want the fat tire look? Buy a bike that comes with one.
The bike handles best with the stock size tires.
But if you insist on looks over performance, you can put a 120 up front and a 160 in the back. IIRC, there's been a member or two that have squeezed 170's on, too.
IMHO, none of these tires will wow onlookers, so might as well stay with the stock size. It may be worth stepping up to a 160 if the tire you want isn't available in a 150 (160's did come on 2G B6's).