In your experience, out of these breeds, which are the most likely to be most protective instinct?

We raised dobermans and rotts, and we had other show dogs as well. After 20 years of dog shows and raising our own I believe that dobies are the most protective. Big babies if raised right but still protective. Our insurance guy had been coming since our last female was a pup, but one day we were not at home and when he came up the stairs to the porch she let him up but wouldn't let him leave. She never barked or growled, but if he tried to go down she showed him her teeth and if he reached for the door she showed him her teeth. she kept him there for two and a half hours until I came home and told her to let him leave. Keep in mind she wasn't a trained dog.