I think it depends on your lifestyle. GSD's and Dobies are good, but most of the American versions aren't well bred and tend to have bad nerves. I would just do a ton of research on guardian breeds and see which would best suit your home. Keep in mind when you own a guard dog you are going to have an animal that views everyone as a potential threat to you and that will include kids and old people. Your dog isn't going to be outwardly friendly with strangers and he's not going to be the kind of dog that kids in the park can run up to and pet. I own one guardian breed, a Cane Corso and one pit bull. We have to keep them separated or else they'll fight.