I think for the welfare of the animals, you should never keep a single of anything. So, the most natural think for ducks would be to have a trio.
Muscovy ducks are considered "quackless". They have come down to us from a wild South American duck and are not related to all other breeds of duck except by a common ancestor. I think they're pretty myself; but some people find the carnucles ugly.
Aside from those, all ducks are of equal volume.... except Call Ducks which are brutally loud and shrill.
well my ducks - used to live with my chickens until one of my drakes decided he would mate with the chickens - so they now have thier own yard. I perfer to give mine a kiddie pool - I think they are happier with water to play in.
My ducks also eat the same thing as my chickens - makes feeding time alot easier !!