I recommend you to go with 18" because 17" tires are getting harder to find! Newer cars is using 18" and up! In 10 years 17" is special orders only!
I have 11 x17 275/40 and13 x17 335/35 on my older Pantera and on the newer one 11 x18 275/35 and 13 x18 335/30 and the tire height is almost same.