18s will give you some pretty bad clearance problems (assuming your car is lowered) unless you roll your fenders. 17s will rub, but if its gonna be a showcar, then you probably wont mind. IMO, 16s and 15s look the best, show or not. Keep in mind 17s or 18s will totally dwarf the appearance of your brakes, so if you want the car to look decent, you might think about a big brake kit.