Triumph's triples in the mid/late 90's were hard to beat. Daytona 900 Super III and Speed Triples (original T309 series) with Arrow or similar 3 into 1 exhaust were an incredible sounding machine. The next generation of T595/509 series could be equipped with an under seat exhaust from Black Widow that had a real nasty/mean/spitting ear assault when run through the gears. Triple are some of the best sounding bikes, period. Next, for me, would be gear driven cammed V4's....like the 86 Interceptor I owned with a full Yoshimura system. It sounded like a small block V8 with a blower.