I've had a number of dogs during my years, and have known a lot of friends' dogs. Seems to me, overall, that for a good "take care of you" dog, a good Shepherd pup, raised in one's family, just naturally is protective of "his" people.
I'm talking here of a dog with little or no training, just following his nature. I don't at all mean to knock any other breed, and certainly understand the value of competent, professional training.
Most folks just want to buy a pup, take it home, and let it grow up in the expectation that all manner of good attributes will just naturally occur. That's just the way people ARE. By and large, a Shepherd commonly seems to come pretty close to filling the bill...
$0.02, Art