I'm still on OEM for the moment, although I did add 20/25mm spacers to look cool.
Considering getting the wheels powdercoated glossy bronze.
When I do eventually purchase wheels, I will go with 17's for a few reasons. First, they're cheaper. So are tires. Wheels might not be a wearing item, but tires definitely are. Secondly, the ride is better. More sidewall = more cushion = better ride. My suspension is firm enough already, thank you. Plus there's that little bit of extra forgiveness to keep me from bending a wheel should I hit a pothole or curb or trick-or-treater or something. Lastly, they're less weight. Our cars aren't super powerful to begin with, so any additional weight, rotational weight at that, slows them down. While there are 18's that are pretty freaking light (TWS), most of their mass is still situated further out from the point of rotation than a 17, which is extra inertia you have to overcome with throttle and brake.
These cars look gorgeous on 18's. I'm particularly fond of
Shiumai's and
Jive Turkey's BRZs, Shiumai with 18x8.5/9.5 staggered, and Jive Turkey with 18x9.5 all around. They really nailed the sizes. It's just not for me.