Gotta say, nothin sounds like a tuber with a Force . I love my S2's sound, even though the motor is stock 9:1 CR. I'd love hear what my dream motor build would sound like... 90"XL motor with Feuling 4-valve heads, 12.5:1 CR, Delphi EFI, twin Race A/Cs and a Force style exhaust!
I'm a fan of how the V-Rod Destroyers sound, after that the new R1s sound amazing...2 completely different types of sounds though. Sometimes I like to feel the bass of an engine, other times I love hearing the scream of sky high RPM limits.
Watching the video Chevycummins posted reminded me of another really great sound of performance. Not a bike but nothing like a P51 Mustang at 400+ MPH rounding one of the pillons, with its Merlin engine screaming, at the Reno air races. Earth shattering and what helped keep us all safe and win WWII. And what a "ride"!!!
I always loved the sound of a 2 stroke racer I will always remember a guy we raced with back in the day had a Maico and it was the coolest sounding bike I ever heard. I would buy one of those today if I could.
A roundcase bevelhead with Contis is about as sweet a sound as comes out of a motorcycle. Beyond that you need a large round engine with a P&W or Wright nameplate, or a v12 that says Allison or RR on it somewhere...