It is hard to pick but I guess I would have to go with a German Shepherd my dad bought when I was a kid of 5 years old. This dog had been trained for a seeing eye dog but failed the course because he had a playful streak that could not be over come. He did his lessons great but when he saw kids playing he was too excited about that so he was sold. My mom said he was the best babysitter she ever had. I could play in the yard without her worrying so much about me. He would not let me in the road. Even though we lived in the last house on the lane and the only traffic was people that came to our house I was NOT getting in the road. Also, there were rattle snakes. He would circle me every few minutes and if a snake was nearby he would grab my wrist and take me to the house. Then he would kill the snake. Once one got close before he knew it and he killed it right next to me. When my mom folded clothes that went upstairs she would put a stack on the stairway to take up when she was going later. She had to stop doing that. Things do not belong on a stairway, they are a trip hazard and Bullet would take the clothes up stairs and shove them in a corner. Nothing stayed on the stairs. Once when I was outside playing Bullet was off in the barn, a dog I did not know came into they yard. Their was a neighbor boy playing with me. The dog bit that boy and had started toward me. I screamed for Bullet and he came running, leaped over my head and landed on that dog. After a short fight the dog left. I was 5, I don't know if they ever found the dog and tested for rabies or not. I know Bullet was fine. Another time after we moved into town a neighborhood bully was, well, bullying me, kicking the spokes on my bicycle and Bullet grabbed the kids pant leg and while growling something vicious pulled the kid away without touching the kid, just his pant leg. Of course the boy was scared and yelling at me to get my dog off him. I ask the kid,"you going to leave me alone?" "Yeah, yeah, I'll leave you alone." Come on Bullet.
I loved that dog. He loved playing foot ball. Would tackle me gently but would take my dad to the ground! He pulled my sled in the winter and wagon in the summer. I still miss that dog.