Don't let anyone fool you!! There are dogs that can have a tendency towards aggression if they aren't socialized early enough, but for the most part ANY dog can and WILL become aggressive if it isn't handeled correctly. The biggest problem that people have is not doing enough research before GETTING a dog. go to the bookstore or library and READ!! just pick up any dog encyclopedia or breed book and they will almost all tell you what that particular breeds needs are. Even so, in each breed, and even each litter of pups, you will have confident, nervous, shy, or aggressive pups. you have to pay attention and know what to look for. If you decide to adopt a dog from a shelter, find out if the shelter will allow you to see the dog interact with another dog, and also bring yours or someone elses child with you to the shelter. Some dogs are VERY unfriendly to children because they were teased or tormented by them and so they bit them and thats how they ended up there in the first place. But you wont know unless you bring a child with you to walk in front of the kennels with you. You'd be suprised how many seemingly sweet dogs turn into Kujo when a child walks in front of the kennel door. Again, if you are a quiet person, choose a low activity dog. Herding dogs and terriers (including pit bulls) , dalmations and boxers, all of these dogs need LOTS of exercise and activities to keep their minds sharp and alert and to keep them from getting into truble. Larger dogs tend to be more docile, and placid, but again, spend time with the liter, or dog to be sure. If you are an active person, then don't get a lethargic dog, you'll be more unhappy then he will. And remember ANY dog CAN bite, but it doesn't mean that they WILL bite, just because of their breed. Also, some breeds need a heavier hand than others. keep that in mind also.
I am a dog trainer and a veterinary technician