There are a lot of researches listing the best guard dog breeds. They are not at the same opinion but here is an overall summarized list based on over 10 studies .
10 American Pitbull Terrier
The American Pitbull Terrier is a result of experimental crossing of terriers and bulldogs. Although usually an intelligent and friendly dog, it has sense for danger and knows when it needs to protect.
Boxers are developed in Germany by crossing the Bullenbeiszer and the Barenbeiszer – two German mastiff type dogs.
An athletic and energetic dog, the boxer is very courageous and is very suitable as a guard dog. It is often used in the police and when trained by a professional (like most dog that are suitable for guarding) can turn into a really scary creature.
8 Komondor/ Hungarian Sheepdog
The Komodor’s origin goes back centuries ago. His forefathers are the Tibetian dogs. It is specially developed to guard his master’s flock.
7 Brazilian Mastiff /Fila Brasileiro
This breed originally developed in Brazil to protect the plantations by crossing Mastiffs and Bloodhounds. The Brazilian Mastiff is extremely self-confident and courageous dog that is suitable for protecting bigger areas. Naturally a born guarding breed , it do not hide his dislike do strangers.
6 Cane Corso – Italian Mastiff
This is a perfect protection and watch dog. His origins are in Italy it has been used for centuries for hunting and guarding. It is very intelligent and trainable and can turn into a real beast.
5 Argentinian Mastiff /Dogo Argentino
It was bred in Argentina from Cordoba Fighting Dog and other breeds, originally for hunting. It is a very muscular and strong dog needing a lot of exercises.
The Bullmastiff was a cross of 40% Old English Bulldog and 60% English Mastiff. The result is highly intelligent, less barking and strong dog perfect for guarding.
3 Doberman Pinscher
Ranked the fifth most intelligent dog, the Doberman Pinscher can turn into a perfect guarding animal. At the same time if trained properly it turns to be ideal family dog.
2 German Shepherd
Very protective, intelligent and loyal breed, the German Shepherd is the second best guarding dog. (Although considered number one in several researches. )
The number one – the Rottweiler is a powerful breed with well-developed genetic herding and guarding instincts. A dog that is eager to work, if trained properly can be a perfect assistant as a watch dog or a guardian .