I would personally recommend a German Shorthaird Pointer. Normally they are used as hunting dogs, yet they make great family pets, and fulfill the protective qualities that you seek. My family got one when I had just turned 3 years old, and 15 years later she is still going strong. They respond well to obidence training, and are very loyal. Back in her prime, and still today, my dog ("Coco")scared off many a mailman and delivery person. She also aided in an arrest once. A robber jumped into our backyard, trying to hide from the cops. Coco cornered him in the yard, snarling and barking, and tiped my parents off to his presence. We were able to call the cops and tell them the guy was in our yard haha. She was, and still is, very protective of me and my brother, yet as soon as she feels comfortable she is the most loveable dog in the world. She has not once nipped at or barked at any family members, including my young cousins poking, pulling, and biting her haha. She is an amamzing dog, and her pups were the exact same way. My grandfather kept one of her pups, and at 10yrs old he is about 100lbs of solid muscle with the loudest bark I have heard from a dog his size. Overall a great dog, one that I feel meets all your needs.