I have muscovies and Welsh Harlequins.
Points I make about my 'Scovies:
*quiet! quiet! QUIET!
*Come in MANY colors, they're all gorgeous.
*VERY calm, can be tamed fairly easily
*EXCELLENT meat birds
*EXCELLENT mommas
*Don't have a mean bone in their bodies
*Easy to care for and relatively clean for a duck
*Free range nicely (and the multiple colors look gorgeous free ranging!)
*They do fly but they tend to stick around if they know where the food/water is, and can be pinioned or have wing feathers trimmed to keep them grounded.
*Some don't like caruncles - I didn't like them at all when I got them. I have changed my mind. The non-show muskies look gorgeous with their bumpy masks that contrast with their rich feather colors. Over-caruncling is gross and silly, IMO, but the 'right amount' looks very nice.
Points I make about my W.H's:
*They make 'duck noises', which is weird after owning only 'scovies for 4 years. We don't have to worry about loudness, here, because we have no close neighbors.
I think the drake noises are some of the prettiest animal noises EVER.
*They are GORGEOUS. They only come in 2 color phases but they are absolutely stunning - both males and females.
*purported to be good layers. Mine were babies from summer 2010, so mine should start laying anytime between now and spring.
*They are more skittish than 'scovies by far - though not annoyingly skittish. This is fine for me, because I don't make 'pets' out of my ducks.
All in all, ducks are AWESOME if you can provide for them correctly. I'd never keep ducks if I kept them cooped or in a run. They are just to messy and smelly for me, in those conditions. Takes way too much work to keep them clean and happy. But if you have a big area or can free range them, they are SO worth it. Keep their food/water/housing spread out, and they don't muck it up with poo or spilled water easily. At least, that's what works for me.