Every dog is different and each individual dog has their own drives and character traits. Each drive is different as are the traits. Dog breeders breed dogs for a specific look or traits desires. Example: Cattle dogs (many different types) Retrievers, etc etc.
Traits: Courage, Hardness, Softness, Sharpness, Confidience, Temperment, Sensory Threshold (amount of stimuli to get a reaction)
Drives: Hunting, tracking, air scenting, retrieve, prey (bite/kill wont let go in tug of war), Fight, Guard, protection, rank, trainability, survival, homing, play, activity and pack.
Drives in dogs can be enhanced or diminished. Traits cant. So you want a dog thats a good family pet (pack drive) will also warn you of intruders, (guard drive) and protect you and family (protection.) A German Shepard is a perfect dog for that. Very smart too. They need room just like most larger breed working dogs do, but if you start your training (obediance early) it will work out well for you. There are several other dogs that meet your same requirements; Mastiffs, Boxers, Doberman Pinchers, Rots, Akitas (tend to be agressive), etc etc. etc.
I have owned several dogs over the years and work with one every day as my partner for work, however, the best family dog we've ever had was one we saved from the pound.