I don't have any experience with chickens, but I love my ducks! We have about 30 right now (includes 18 ducklings to be sold). As for keeping chickens and ducks together I've heard of some who do and some who don't, the latter being because the ducks yuck up the water so bad and chickens don't appreciate that. :)
I agree with the others about the mess and noise, although it's only the females who have the loud quacks. Drakes have very low, raspy, "whisper-y" sounds. I also agree to not keep just one, get at least two.
I don't find them to be high maintenance at all. Ours free range 24/7, have a pool and a pond. In the summer I only put food out twice a day because they forage all day long making them excellent bug control.
Stella - sweet, timid, elegant, lovely, lively, amazing
Luna - large, unattractive, naughty, adored