Re:The Best exhaust system?
 

The best is always a muffler that you can look through and see out the other side. My personal favorite exhaust ever is correctly-sized pipe to a Walker Dynomax muffler to a rolled-back tip. The Dynomax acts like a resonator, kinda loud, but very deep. You have the right sized pipe if when you are backing off at mid to low RPM and at about 25" of Vacuum, it hits a bass note that makes your ears pop. The roll back tip amkes it do funny things when you shift. :)

Re:The Best exhaust system?
 

my little brother has a MBRP cat back on his focus ZX-3, really low sound and almost stock sounding at cruising speeds