The German Shepherd mix that was the first dog my family had when I was a kid was by far the smartest dog I've ever met. She knew when to be protective and when not, how to bark politely or how to be scary, and knew the differences between toddlers, children and adults. She was bonded to the whole family, not just one person, and my family got her when she was already an adult, and she had been a stray, so it's not like she went through a lot of formal training!