I am a firm believer in AR's for coyotes. I have used an Olympic Arms K8, 22" Remington R15, and a 16" Bushmaster carbine. They have all been reliable and accurate. My opinion is that unless you are looking to stretch your range really far, you may appreciate a shorter and lighter barrel. The longer and heavier barrels are great for higher velocity and accuracy, But, a free floated 16" barrel can be very accurate as well while saving a lot of weight and length.
I think that covering a lot of ground is critical to coyote hunting success and saving weight helps you do that and net more dogs. I have come to prefer my 16" bushmaster with a free floated govt profile barrel for general predator use. This setup has proven accurate and powerful in my experience. I have shot the RRA ATH and predator pursuit: I think both are great setups, just a little on the heavy side for my taste. I have no experience with Daniel defense but they have an excellent reputation.
My ideal 300 yard coyote AR would be a free floated 16" barrel of a medium profile with a good trigger on it and a quality scope in the 3-9x range. Handy, Light, Accurate, and fast.