Best and Loudest are two different categories....If you want Best...than it all comes down to your personal preference...What's best for me may not be best for you...Now if you're looking for loudest...than I have to back up AK on his recommendation....The Meisterschaft GT Haus Exhaust is the loudest there is out there...Hand Down!!!!
Best IMO...
and My Opinion Only...is Berks or FI...Again...this is based on my personal preference.