That's a tough question and there are lots of opinions out there. We have a German shepherd but he has killed a duck and maimed one but no chickens. They don't "squeak" like a toy. My aunt has a German shepherd that will kill a chicken if she gets the chance. I, personally, think a puppy would be wise. So far, the ducks have been our only casualties.
I'd research the different herding/flock dogs. There are lots to choose from. Some shed some don't. Some are big some small.
Good luck