United, an Australian franchise (usually run by Indians) has the best quality. Then Caltex. Problem with Caltex is its origin and strength is typically less than 70% pure.
with regard to your last question with exhausts,i am happy with the system I have which is pacemaker extractors flowing to a 2.5inch catback all the way through,i currently run redback,the sound is reasonably quiet until you put your foot down which is how I like it,keeps the boys in blue away-lol