Dobermans have a sense of self preservation that other dogs (i.e. GSDs) do not. Dobermans typically will not endanger themselves or hurt themselves knowingly. They are smarter than that.
I believe that this is the mantra many Doberman people adhere to when the real issue is the overwhelming tendency for the breed to be lacking in nerve. I will say it again, while it is true that a dog in fear is thinking of its own self preservation first, it is not because they are smarter, it comes down to an issue of nerve. Most Doberman's are lacking in nerve.
As far as GSD's, even there, only a trained working line dog who also happens to have high nerve is likely to stand its ground. Most GSD show dogs, GSD byb dogs, or thin nerve working dogs are going to run away just as quick as the average Doberman (or Malinois) in response to a DIRECT threat.
A working line Doberman is no piece of cake- mine is more work than I could have ever imagined and I did a TON of research, meeting, and talking to other people. I would not suggest a working dog to someone unless they were actively working them, and I wouldn't call personal/property protection actively working. As a side note- Schutzhund is also not a sport for someone wanting a protection dog in my opinion- it is routine based and not situation based.
Any Schutzhund training regime that trains primarily to the routine is crap training. On the other hand how many real human threats are going to be making tons of prey movements, clattering sticks, yelling etc. A decent dog does not view this as a threat, it views it as prey attraction.
Bite sport training, if done effectively and with proper forethought can lay the foundation for an effective personal protection dog. It would only lay the groundwork however. Excellent protection training works on maintaining balance in drive of the dog. I agree that probably most Schutzhund training regimens as well as most Ringsports training (at least from what I can see) are training almost exclusively in prey, though not all do. There are a few training helpers out there that try to bring out the real deal in training. Good dogs who are trained in this type of training are going to exhibit much more power in the work. A lot also comes down to the dog. When we have a very high nerve, prey oriented dog, we will do everything possible to make it about the man not the sleeve. This is achieved through working the dog in conflict or using a bite suit. Dogs that are balanced in drive or going to see a balance in the work. A dog that is always in conflict or defense oriented is going to be worked primarily in prey.
Any honest half-knowlegeable person who trains in any of the bite sports will tell you that real personal protection training is a whole different mode of training that the dog and handler will likely have to train in to have a good chance at reacting properly to a real life scenario.
In addition if you want to get financially fleeced or being exposed to training that is detrimental to the dog then pick from all of the personal protection trainers, and probably 80% of them will help you out there.
Like anything else on the internet finding the right dog, the right training scenario, etc takes sifting through a ton of BS. The best thing is to visit training clubs, whether that is Schutzund, Ring, or whatever. Talking to people there is where you will get the best information regarding where to buy dogs or puppies and finding an ethical personal protection trainer, if there even is such a thing in your locality.
As far as the other posts. Just because a dog alerts to a threat does not mean they are "a natural protector" and will actually protect you. The belief that the Doberman is a natural protector is a myth. Most will run from any real threat.