If you haven't lowered it first, do it before you buy rims. Stock height and new rims don't mix. Trust me...it looks hella ugly. I would say drop it like an inch or two. Nothing major but enough to get rid of some wheel gap, but not too much to have your tires rubbing.
Now if you want to have acceleration, I'd personally go with 16" rims. Those seem to be a happy medium. 15"s seem to be too small and 17"s are bigger and heavier so it takes more to move them, thus lack of acceleration. If you want 17s, make sure you get them as light as possible. This will help your accel. But if you just want show, get whatever you like.
Someone else please feel free to say whatever I didn't
Or correct me :finger: