Which dogs are most apt to exhibit aggression?
When it comes to owner-directed aggression, male dogs are more apt to have the problem than females. That’s especially true if they’re intact. Neutering decreases owner-directed aggression by 25 to 30 percent.
Specific breeds that tend to be brought to the behavior clinic for aggression, at least in one study conducted at Tufts, include German shepherds, cocker spaniels, and mixed breeds. At Cornell, some research has suggested that springer spaniels and rottweilers present relatively often for aggression directed at their owners, while German shepherds are more apt to exhibit aggression toward strangers.
The least aggressive breeds, again, in one piece of research: Golden and Labrador retrievers, Bernese mountain dogs, Brittany spaniels, greyhounds, and whippets.
But these are trends observed, not facts about any particular breed engraved in stone.