Maybe you are looking to get a new puppy for the family pet and would like to know which dog breeds may not be the best with children. After doing much research, I have compiled a list of the 10 most aggressive dog breeds. In doing my research I have found that different organizations as well as different âexpertsâ have their own opinions as to which dog breeds are the âmost aggressiveâ. The ratings, as far as which is the most aggressive, vary as well. The dog breeds that I have listed here are the breeds that have been ranked as the most highly aggressive, most frequently. The percentage of the test results I have included are from the American Temperament Test Society.