I have seven millie d'uccle chickens, two Cayuga ducks and four Indian Runner ducks. They are mostly apples and oranges in my opinion.
Ducks are very hardy, they don't typically need heat lamps in most climates. They can survive on grass and bugs, with little other feed necessary (although I spoil my ducks and chickens with a very wide diet: brewer's yeast, granite grit, free access to fresh grass and fresh bugs, layer feed for the birds who are laying eggs, flockraiser, un-medicated sratch, and dried mealworms). I keep them in their own, low-built houses every night, and I keep the two breeds in separate houses because they have very different temperaments and wouldn't get along in a confined space. They have a kidie pool to swim in, drown parasites, and clean out their nostrils (important to avoid pneumonia and infections). Many duck breeds (and some chicken breeds) do not brood - they won't sit on a nest of eggs.
Chickens, on the other hand, have very different needs. I keep a light on for them in winter; they are less reistant to the cold than ducks. Ducks have more insulation (since they spend most of their time in the water). Chickens are more susceptible to diseases and parasites, and you should provide a sandbox for them to bathe in to strip parasites off their feathers. They do not require a pool. Their food requirements are different too: many chicken feeds are pre-medicated, so you never want to let a duck eat chicken feed (this means you should never keep ducks and chickens together: you don't want the ducks eating medicated chicken food, and you don't want the chickens to transfer any parasites to the ducks). The chickens do not need brewer's yeast. You will probably have to provide some kind of parasite management at some point; I use a liquid spray I got from the feed store to spray the coop when I clean it out. I do not use poultry dust because it's a harmful chemical to pretty much all forms of life, and toxifies drinking water if it gets in the ground (and we're on a well, so there's no way I'll use that nasty stuff)...plus, if I wouldn't want it in my drinking water, why would I put it on my chickens?
In terms of personality, I've found chickens to be more skittish than ducks...most of that can be alleviated by spending many many hours with them when they are young, and associating your presence with food. With ducks, it really depends on the breed, and the level of attention you give them when they are young...my Indian Runners act like chickens: everything is an emercency to them, everything scares them. The Cayugas are opposite...I can walk up to them and pick them up no problem. I raised all of them from very young babies, but they have very different personalities. Both fit in on my small farm...the chickens wander out in the pasture keeping the sheep company, and the ducks hang out near the house and waddle about entertaining us.
