What do you want ducks for? Meat, eggs, eye candy?
Meat---Pekins, Rouens, Silver Appleyard
Eggs---Welsh Harlequin, Khaki Campbell, Cayuga (black eggs,) Silver Appleyard, Swedish
Eye candy---Call, Welsh Harlequin, Silver Appleyard, Swedish
Ducks come in about a million different colours, all of which are gorgeous. Khaki Campbells are probably the plainest duck out there and even they are pretty brown tones. My personal favourites are Welsh Harlequins. They're a nice sized duck, sweet, pretty, and absolute power layers. You might just trade them for chooks.
I feed mine chicken layer pellet once they've matured, never had any issues. Just place feed far enough away from water that they can't turn it into a soup.
When they're growing I hear Purina All Flock crumble is the best if you don't want to bother with supplementing niacin. They get scraps, same as the chickens, but watermelon is probably their favourite in terms of treats. Make sure they never have feed unless they have water too. Oh, and their water needs to be deep enough for them to clean their nares and eyes.
One tip... do not raise ducklings in brooders. I will repeat it.
Do not raise ducklings in regular brooders!!
They are messy little feed guzzlers and will turn your clean shavings to paste in three seconds. Get them to 1 week of age in an indoor brooder and then put them outside on grass in a safe pen that can be moved daily. You will be SO glad you did this. Oh, and for that first week, sand works great.... if you have enough time to scoop it daily or twice daily. If you don't have the time, it turns into a stinking soggy mess.
For adults, free ranging really is the best. Ducks are messy-messy-messy and space helps keep maintenance down. A kiddie pool or two or more is good for summer, it keeps them happy, healthy, external parasite free, and they're less likely to murder your garden that way. No guarantees though. I have found them to be worse than chickens with destroying flowers because they tug and pluck and root rather than just peck and scratch.
Edit: ducks don't require near so much heat as chooks. Mine were off heat by 1 1/2 wks of age & didn't use it much even before then.
What exactly does this mean?
Ducks require a lot of protection from predators, especially the breeds that can't fly. They are slow runners and don't roost, meaning they're the first to go when something breaks in. Guess how I found that out?
Dogs, coyotes, foxes, hawks... they can all wreak havoc on ducks even moreso than chickens. My ducks are smart now, they hang around the woods and watch the skies, so I haven't lost any to hawks yet, thank goodness. Oh, that reminds me---put pools within easy running distance of cover.
Ducks are hardy little beasts and rarely get sick. Just keep an eye out, they should be fine. Oh, the heavy breeds are more prone to bumblefoot---check on those webbies frequently.