What's a better guard dog? A Doberman, a German Shepherd, a Rottweiler, a Great Dane, or a Mastiff? Help!!!

From the choices you have there, its a rottweiler. But the best guard dog you can get is a pit bull

Most of the dog breeds you mentioned will naturally act as guardians when at home, but some dog breeds have been especially developed or selectively bred for their natural inclination to guard and defend the territory and people they consider as having under their custody.A panel comprised of dog breeders, veterinarians, and dog trainers have established a list of dog breeds especially suited for guard dog duties. Dog breeds that qualify as guard dogs must possess a natural inclination to protect along with a strong sense of territory. They tend to be wary of strangers. They stand out for their courage and their resistance to counter-attack. Other qualities considered as essential by the panel were: trainability, loyalty towards the owner, stress-resistance, watchfulness, and the deterrent factor. The deterrent factor includes not only the impression an individual dog makes because of his bulk, voice and color (black is more impressive than white) but also how recognizable the breed is as a guard breed. A Rottweiler or Doberman will be more easily recognized by a would-be intruder as a guard breed than an Akita or cross-breed, for example.The list this group developed is as follows and may cause you to look at your choices a bit more broadly.1. Fila Brasileiro2. Rottweiler3. American Pit Bull Terrier4. Doberman (females moreso than males)5. Dogo Argentino6. Belgian Shepherd Dogs 7. South-African Boerboel8. German Shepherd Dog9. Cane Corso10. Presa Canario (of Diane Whipple/San Francisco fame)11. Tosa Inu12. Neapolitan Mastiff13. Dogue de Bordeaus14. American Bulldog15. Ca de Bou16. Bouvier des Flandres17. Giant Schnauzer18. Thai Ridgeback19. Bull Mastiff20. Akita InuKeep in mind a dogs size can also limit its ability to maneuver. Great Danes aren't on this list for that exact reason. Though large, they aren't known for being the fastest dog on the block.I have 2 Dobermans, so my vote would be in that direction. They took to protection training, and it takes just one word to put them in that mode.And before people wig out, a Doberman trained to use what they do instinctively is FAR safer around strangers than one untrained.

Rottweiler.Rottweilers's eyes are a warm, dark brown.waterproof undercoat.A well-trained and socialized Rottweiler can provide the right owner with a great deal of exercise and loving companionship.They are intelligent, to the point that they shouldn't be left to their own devices, and are happiest when mentally stimulated.The Rottie is not usually a barker: he is a silent watcher who notices everything. The female, however, may become a problem barker in order to protect her den. In the event the dog feels threatened, he tends to go very still before attacking, and there is no warning growl.When the dog barks, it is more of a sign of annoyance with external factors.