You want the yard mowed, you gotta go with the aforementioned vicious geese.
Mine are big fat sweeties that lay big fat dumps all over the place. They are still downy, but are getting their feathers in. They are already larger than my standard ducks, including my big fat Rouen.
Speaking of Rouens. AWESOME. Mine is quiet, big, an excellent layer of large eggs, and friendly. The friendly part might ruin the whole "meat" thing for you depending on how soft your heart is.
Welshies. Best ducks in a group ever. Quiet, excellent layers. Varying sizes. Unless you want ducklings, skip the drakes. They are just trouble makers.
Personally, I'd go with Craigslist. Ducks aren't really disease carrying like chickens, and getting an adult duck is great, especially the first go around. Ducklings are adorable, but they are seriously disgusting.
I can't speak to Muscovy ducks, but people really seem to love them! I hear nothing but good things about them. If I could get past their ugly faces, I might try some one day.