In terms of numbers, over the 18 years I've had chickens, raccoons and red-tailed hawks have taken the most. Raccoons stopped being a problem after we switched to electric netting, but the new location lacked cover and so hawks became a much bigger threat.
However, the worst predators I've had experience with are dogs and man. Wild animals will try to eat chickens, it's just a fact. You can't blame them for it, they're only doing what's natural to them. Dogs should either be trained to be livestock safe or kept under control. There is no excuse for someone else's dog killing my birds, and I find it much more intolerable than them being eaten by hungry wildlife. When I was a tween, the neighbor's dogs got out and broke open a chicken tractor full of 8 week old pullets that were growing out. We spent hours counting the dead and finding/catching the poor terrified survivors that had scattered across the acreage, making me late to my own birthday party. The neighbors are lucky those dogs never did anything like that again, or the problem would have been taken care of.
And of course a person being cruel to animals is always unacceptable. The only time that ever happened to us is when some stranger open a chicken tractor full of CX for seemingly the sole purpose of drenching them in antifreeze and spraying them with silver spray paint. We never found out who did it, but luckily after some time spent bathing the poor birds, the majority survived. We only lost a few, who likely drank the antifreeze laced water. However, the fact that they were contaminated meant that we could not in good conscience allow them to be eaten, making it both a waste of dozens of lives, and a significant financial blow to my family, as chickens were one of our main sources of income. The trauma surrounding that event is a large part of why we quit raising them.
So while more total birds were lost to hawks and raccoons, they were far from the worst.
