Yeah, I think I'll skip all the friction, drama, etc. that this very simple question seems to have "empowered".
The ANSWER is "Bassani". Darryl made a 4 into one that (1) gave excellent ground clearance (2) didn't get in the way of the oil filter housing or the oil drain plug (3) came with a "racing only" (ha, ha...) alternate tip (4) made better power than stock was lighter and was hardly any louder. Oh, and (5) it didn't require that you remove your centerstand.
It also wasn't as aggressively marketed as Kerker, RC et al. It was still the best, though - even unto this day. And yes, though this will seem like heresy, it was better than - gasp! - the Yoshimura pipe, which required all sorts of compromises since it was a mildly reworked race exhaust. Darryl's was designed as a street pipe. Just sayin'. My opinion only here. Not a diktat or a polemic. Please don't be offended. Wait - be offended if you have that much free time!