We have 5 ducks and 4 chickens. They get along fine, share food, water, the run, everything. They have their pecking order with the alpha hen and the alpha duck and then there is the drake who is kind of top bird. We don't find the ducks particularly messier than the chickens in general, but they are klutzier, so more spilled food and you cannot keep anything around them dry. They have their own houses at night, but lately, the ducks seem to want to hang around in the bottom of the chicken coop at night. As long as there is no food or water in there, I don't see them making it any messier than the chickens do.
Chickens are kind of oblivious to everyday stuff, very friendly, love to hang out with you, sit on your shoulders, back, or head, but the first to investigate anything new. Ducks are similar, but much more wary of new situations or new things coming into the run. Very affectionate and love to cuddle in your lap and what I call schnerbal....using there bills to nibble at your clothes, laces, boots, fingers, ears, hair. The chickens tend to peck and while they are not hard pecks, they can be less gentle than the ducks.
Ducks are LOUD, except for the drake. Not all the time, but when they get going, it can be deafening. We don't have near neighbours, so not an issue and they mostly quack when they get excited, like when we come around to let them out of their house in the AM, come with treats, or just come out of our house in general. They greet you. Hens are quiet, they just murmur and mumble and cluck softly.
I love them all. It just depends on your circumstances.