You all seem to agree that Dobermans & Rotties are great ?

Guard dogs. I have always seen Dobermans as slightly bigger whippets. I understand that they were bred for guarding alone. I have seen all the films and know how good they were in Wars and for the police but they just seem so skinny. Why are Dobbies rated so highly? Surely you would rather have a Rottie, Corso or Bull Mastiff- What are your thoughts?