Predators will be happy with what ever you chose.
Both ducks and chickens will need to be penned. Chickens take more to keep them in, as they can fly, but ducks are way messier. Chickens can be kept in tractors and moved about and free ranged if close to the house and you have non-chicken eating dogs to keep varmints at bay. If not using chicken tractors, (not good if predators are bears and such) than a good solid coop and run is best. Electric wire around the whole shebang will help deter larger predators like bears who can destroy the set-up in minutes.
Ducks need quite a lot of water which they like stinking up and spreading about and if confined, this water also goes into making a stinking mess in the summer and a frozen poo skating rink in winter which then turns into a stinking mess in the spring. People have had good luck with a fenced pond with a duck house on a raft in the middle of it.
If stocking ducks, the right breed is essential, as many are seasonal layers. An egg every day for around two months in the spring and than nothing until fall when the same may occur with some of them. One duck egg is equivalent to two chicken eggs. The yolks are huge with a smaller amount of white in proportion. Duck eggs are very rich compared to chicken eggs and the whites are firmer in texture. Try one out before deciding to buy ducks. Others have commented on what they think of duck meat so I won't.
Ducks basically provide you with two breasts and a carcass for soup. You probably already know what you get from a chicken.
Ducks are really good at brooding although they have a problem hoarding up to three doz. eggs in a nest and than either having them all rot or all hatch. You may end up with 23 ducklings and find that all live, or more likely, that most of them die getting lost/left behind on the way to the pond, or simply stepped on by another duck. Its all a lottery with ducks.
I have both ducks and chickens and it is the chickens that will be staying if I have to tighten my belt any more.