With the right setup, DUCKS. By a long shot. So long as they've got a good water supply, and a safe place to sleep, they are amazing critters.
The eggs are amazing, and my ducks far out perform my chickens. They lay longer into the winter season without supplemental light, and I've noticed that they are reliable layers well past the third year mark.
They don't care about rain, snow, wind or cold. Nothing stops them. They are hardy critters. I have yet to lose a duck to illness. This includes ducklings.
Their poop isn't hot so it can be applied directly to the garden, which is great because there is a lot of it. Speaking of the garden, they are the best with winter cleanup detail. They keep the grass clipped, de-slugged, and the beds weeded all winter.
They are damn adorable. Yeah, that's shallow, but it counts. I could watch them for hours. Duck social structure is pretty neat to observe.
I might be a hair bias. I have a pet call duck sleeping on my lap as we speak. She's absurdly cute.