Which dog breed is best to protect chickens?

we always have bull breeds... we found they are easier to train when it comes to other animals...

I was looking into a good dog to protect my backyard chickens from the hawks, and sometimes we get a fox. I wanted a pyr. and my husband wants a shepard. I would like to get whichever wold be the best for the chickens. I do want to say though, that we had a great pyrenese growing up. And his name was King. He once dragged a baby off the road into a yard from an oncoming car. The Mom watched at first in horror, then quickly realized what had happened. This dog would walk next to us walking up the road and with each stride pushed against us until we were on the sidewalk. He actually broke up dog fights with a couple of barks, and sat down while the other 2 dogs that were fighting ran in oppisite directions. The breed is awsome, and I really want to get one. Since they dont' mind cold weather, I would not mind him or her being out on a winter day with the chickens. I am seeing alot of posts saying the pyrenese is a good breed that protects farm animals which is great to hear. Looks like I may be looking for one.

....I know you have to watch heelers, their nature is to control at all cost and chickens don't herd too well.. Grandparents free roamed maybe a hundred egg layers and had a large old shepherd breed dog, not German Shepherd,...he took the task of keeping the birds off the porch and out of a perimeter around the front yard that he imagined to be inviolate for chickens. He was fantastic about his work, and on command he would go to pastures and bring in the cows for milking, even separating the ones that were not being milked and holding them back until the wet cows were in the barn stalls. I loved that dog.