I am currently in the process of switching out 18's to go with 17's. I had 18x10 and 18x9 and was running 315x30 BFG drag radials on the rears and 265x35 street radials on the front.
I switched primarily because I wanted a set of chrome rims on the car. I went with 17's primarily because that was what my budget would allow following selling the 18's. However, I also like the look of the fatter (taller) tire. And the ride quality is a bit better with the 17's and it helps prolong the life of other parts when the taller sidewall helps absorb some of the punishment from the road.
I will be going with BBS RX's in chrome with 275x40 street tires. If I want to have a staggered look- Nitto 315's fit fine on the back if you are running a 17x9 rim.
These will be the new rims-