they all are pretty good, it mostly depends on $$$ and how loud you want it. if you want loud and cheap(sorry "inexpensive"
) get a off road h pipe and weld some flows into your current cat back. if you want a more exotic sports car sound get a x pipe with a flow through type muffler(ie. dynomax, borla) they both help performance, it's more of your taste in the sound you want
hope that helps
leon
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96 stang,ported 99 heads, 99 intake, 99 cams,Steeda power pullies,Kirban adj.reg.,Pro-m 87,24#inj.,70mm t/b,BBK longtube headers,Bassani x-pipe w/cats, Dynomax ultraflow catback,iat mod, home depot ram air, k@n,373's,cobra brakes,fms spings, tri-ax shifter.
best et 13.80
best mph 103.3
bfg street tires,bakersfield, ca