16. Saint Bernard
Saint Bernards are among the world’s most popular breeds. Native to the Swiss Alps, these huge dogs are famous for mountain rescue missions in freezing temperatures. Females weigh 120–140 pounds, males 140–180 pounds, and may not realize their own strength. Though usually gentle and smart, they can become aggressive if not socialized. What children find funny can quickly turn dangerous, so training is necessary for this and many other breeds.