My vote is for
EUROPIPE. We install them on the Turbos that come here and they are AMAZING! I've driven behind cars with the system and the sound is like nothing else out there. You can here the turbos spooling anytime the driver touches the gas. There is no drone, and the quality and craftsmanship are second to none. They are a little on the pricey side, but they deliver the whole package; great sound, great look, great quality, and great power(~30whp over stock).