Ducks are MESSY!!! I have three ducklings and five chicks and the ducks poop 2-3 times as much as the chicks. And they are big, wet, often projectile poops too! They also string water all over the place. I have my ducklings in a large rubbermaid tote and need to change their pine shavings twice a day (but usually only get to it once!).
That said, they are cute and adorable and have endless personality. I will probably be locked out of this forum for saying this, but I could easily chuck all the chickens out the door right now and just raise ducks. The chickens act like we're going to murder them in their sleep, even though they've had the same attention the ducks have, and when I take them out they just stand around like "duuhhh, what do we do now" whereas the ducks come to the brooder and peep for us everytime we walk by and when we let them out they run back and forth and nibblle at our clothes and let us pet them.
No, they don't need water to swim in but they absolutely love it. I'm just going to get a kiddie pool and build a little ramp up to it.
The ducks seem much hardier than chickens and from what I've read in "Storey's Guide" they are susceptible to a lot fewer diseases than chickens and can withstand cold, wet weather much better. They don't need the fancy housing, just something safe and secure and an enclosed run if you have overhead predators. If you get the right breed (Khaki Campbells bred for egg production) they can produce a lot more eggs in a year than a chicken.
I can't help you with breeds except to say we have a black cayuga, a magpie and a blue swede.