Here's my opinion: (
free with purchase of a**hole 
)
It really depends on the overall look you're trying to achieve with the car.
By themselves, the Zele skirts get my vote for the right blend of aggressive and sleek. The EVO-R skirts are great if you want your car to have the look of a carbon fiber undertray. I don't think the Amuse would work unless you did the rest of the kit. I hate fake holes, so the IMPUL is a no.
The Stillen piece is nice, too. The Nismo pieces are a good choice if you want a factory-tuned look.