I've seen people with very good and impressive GSD's. I don't care for the breed. Got bit by several (at different times) when I was a child. Every single time, the dog stayed away while I was facing it and then raced in to bite me in the butt when I turned to try to leave. Left an unfavorable impression of the breed. Based on top specimens of the breed, I have no doubt that the ones that I met that acted crazy were the result both of over breeding and ignorant people breeding dogs.
The problem with AKC in the US isn't just people breeding to an unreasonable breed standard. A standard that often ruins a working dog breed for working. That's only part of the picture. What's worse is when the breed becomes popular and you suddenly have people with no knowledge breeding the dogs everywhere. When Dobermans became popular, you had people thinking a nervous, neurotic dog was breeding material. After a few generations of breeding neurotic dogs together, you suddenly have psychotic dogs. I've seen Dobermans that hit the ground on their backs urinating on themselves when I stomped my foot and yelled at them. Pathetic. Imagine the owner's look of indignation when told the animal should be neutered if not euthanized. Be very careful when buying any registered breed in America that has gone through an extended period of popularity. Look for a knowledgeable breeder that understands and appreciates the original working origins of the breed over the AKC standard. They are out there, it just takes some searching.
However, there is a problem with Dobermans from top lines. They're predictable. They move in patterns. I raised several litters over the years. Tussled with them, played with them. After several years, I realized that even strange adult Dobermans when attacking were moving the same way as the ones I raised. That predictability will let someone who is very familiar with the breed, clean their clock. I've raised Rottweilers too. I won't take the liberties with a strange Rottweiler that I am willing to take with a Doberman. It's not a matter of being faster than the Doberman. It's a matter of being able to start a counter before the Doberman starts his attack and beat him to the punch. One easy counter to this is two Dobermans. I can handle one up close and personal. I wouldn't try two
Two things I haven't seen addressed in the thread is faking the guard dog off and poison.
I prefer females to males. In my experience, females seem to be more intelligent, more easily trained, and much less stubborn. But the primary reason I like females for guard work is that they cannot be decoyed by a bitch in heat. I've no doubt that exceptional trainers working with exceptional dogs can-with extraordinary effort-train guard dogs to ignore bitches in heat. I prefer to avoid the problem by just going with females to begin with.
The other issue is poison. If someone really wants into your property guarded by dogs...they're going to poison your dogs. And it really sucks watching your dog die from the poisons most often used. BTDT. Training to poison proof a dog is fairly simple. Basically you train the dog so it won't eat except from a certain dog bowl. Then you secure the bowl except for feedings. It's been a good while since I've done this training, I'm not up on current practice-so I won't go into details. I'm sure Sgt. Stevo can tell us what the current state of the art is here.