Have raised MANY guard dogs over the last fifteen years including Pyrenees, Anatolian, Akbash, Komondore,and Merrema along with Australian shepherds, border collies, blue heelers, Catahoulas, and Corgis. We have Cattle, goats, chickens (lots of chickens), and horses. We have seen some good and some bad from all of the breeds we have had and all of the crosses between. If I had to pick just one as a guardian I would suggest the Pyrenees/Anatolian cross. Keeping in mind that how a dog is raised is just as important as what breed it is. Without the propper socalization, exposure, and direction, any dog can be "to aggressive" toward people. For us, the Pyr/Anatolian cross has been the most reliable and trainable.