Moving/retiring to the country lifestyle has been an eye opener for me in a number of ways as it pertains to this thread. First, I haven't seen a link between aggressive behavior and breed of dog. Second, even family pet dogs will kill/severely injure livestock if running in packs. Third, people who drop off the family dog in the country, with the thought that some nice family will take in their pet and care for it, are actually signing the dog's death warrant.
As an example, this past spring I came across a schizuh <sp?> that had, more than likely, died from heat and dehydration. Three Great Danes, two large and one smaller, all died w/i a few days of each other, one was hit by a car and the two remaining by mountain lion. On my property a large mastiff was leading a pack of dogs when it was broadsided by a mountain lion.
While walking in town some years back, two pit bulls jumped a fence and charged me on a fast run. The owner and kids were screaming for them to stop as I braced myself for a hit whilst gripping a Colt XSE. The pit bulls came to an abrupt stop, I didn't have to draw, but I did have dog saliva all over my leg, it was very close.
Another pit bull encounter in Tucson found myself between my p/u and friend's front doorway. Not knowing what to expect, I clapped my hands and said, "Come on boy!" We played for a few minutes and then we went on our separate ways.
I've had a number of encounters at my place, dogs, coyotes and even raccoons can all exhibit unpredictable behavior with humans, and especially so with other dogs.
In the below pic there's a large yellow dog just to the left of the t-post;
It shadowed me and a basset I was tending. It was later confirmed that it led a pack that had had killed pet dogs and goats. Once the word was out, its days were limited.
On one occasion there was an unknown breed of dog that had walked up to the dog pen and lunged at my hand as I was watering the basset. Only the wiring saved me from injury, not responding to verbal commands to leave, I fired two shots into the ground and it ran away. While taking a walk out back, the same dog had circled around, came out of the mesquite and at a full run at me. This time a single shot to the head, less than ten feet, from a Colt 38 Super ended the problem.
Each encounter is different, a little common sense goes a long way.