call me bias, but nothing sounds better than a three rotor at 9000+ RPM's, especially one with ITB's and a nicely built exhaust.
pretty much any rotary with a straight pipe though, usually sounds like shit, they need a few mufflers to make them sound good, they'll be loud regardless.
as far as engines that sound bad, i always hated ford V8's with loud exhausts, they sound like they're underwater!! *gurgle gurgle*