The way a dog acts is almost always a direct consequence of the environment it was raised, not it's breed.
I am not about to tell you that pit bulls and dogs of that nature are for everyone. Some people like small dogs, some people like big dogs, some people have the time to take their dog to the park or have a large backyard, some live in an apartment and do not have the free time to walk their dog five times a day. All of those situations can be adapted to include a dog if you wanted, but it takes effort, consideration, and the right kind of dog.
If you meet a particularly "scary" dog, odds are it has not been raised properly. Some dogs were raised to fight or to be guard dogs, and some dogs were babied and think that, despite weighing the equivalent of a small child, they are lapdogs. So, if a dog is mean, maybe do not jump to the immediate conclusion that it is the fault of the dog or because it is "one of those breeds", because let me assure you that is not the problem.
Dogs are like people, they have personalities and needs, and if those personalities and needs are not nurtured and met it will create an unhappy, otherwise described as bad, dog. If a child misbehaves it is typically blamed at least to some degree on the parents, as it was them who raised the child. Think of dogs like a child, only dogs can not talk so they cannot explain to you if you are doing something that is unsettling to them or they are hurting, tired, or hungry.
The kind of pet you get is completely up to you, I am not going to force a specific breed of dog on you. Just remember that big dogs can be some of the biggest, gentlest babies you will ever meet, while little dogs can be aggressive and downright rotten. Either way, unless it is a random dog you found on the street, how that dog is treated is out of it's hands. Keep that in mind the next time you want to generalize an entire breed.