My Cayuga is the quietest and has the lowest pitch quack, but some people say they are the loudest of theirs. My WH isn't too loud either. My mallards are very quiet except when I first go out to the pen. I don't know if they're sounding an alarm or anticipating treats, but they do this loud high pitch short burst of quacks, and then they're done.
My pekin was the loudest and chattiest. My buff is loud. My runners are loud. I believe calls are very loud too.
So this is where my John Hancock goes? Oh wait, John Hancock? Pffft...it's Herbie Hancock ;]