I agree that it's about the owner, BUT, there are breed differences. I got a lab mix after having a border collie/gsd mix, and the difference is HUGE. It's not just those two dogs, either. I've met quite a few, and breed tendencies absolutly exist. A golden retriever needs loving and compainionship, but other than drool and jumping, you can mostly ignore all training/walking/etc, and get away with it just fine. A german shepherd (or any other fighting or working dog) needs constant training, mental stimulation, and exercise. Slipping on its behavior instruction for even a short time can have disasterous consequences. Those are very hands on dogs. They are bred to be. I mean, that is the reason for different kinds of dogs...they are used for different things. Having a bull fighting dog cooped up in an apartment is a very bad idea. Did you know that pit bulls were often called "nanny dogs", and protected the children? They are very loyal. But...they still need a lot of attention and training.
Yes, labs, etc, can and do bite, and, I believe they are, actually, statistically the worst. I suspect that is because they are generally docile, however, and people let their kids all over them. Or, perhaps, the statistics are skewed because a lot more people own them? I don't know...I honestly haven't looked into it enough.
My point is that, yes, all dogs are a concern, and it really is how they are handled, but there is a significant aspect to breeding and training. As such, I would not be happy with a pitbull, gsd, or any other high energy breed. Even if you have several good meetings with this dog, I would not trust it alone, period. The daily situation changes so frequently with that type of dog, that they can be "keyed up" from being crated, or whatever, moreso than a calmer breed. The fact of it living there would be okay. The shared yard. Not at all.
If you are not a dog person, I would suggest that you get a few books on dog mannerisms, and get a feel for what a dog is trying to communicate, and how to appropriately respond. The Other End of the Leash (Patricia McConnel) and On Talking Terms With Dogs (Turid Rugass) might be good places to start. For example, when a dog is displaying aggression, looking away and yawning, licking your lips, and relaxing your body posture tells the dog you are not a threat. Trying to bend down and talk soothingly to it, and reaching out your hand, however, can seem very threatening to a dog. Facing a dog and telling it to come often will not work, but turning and walking while saying come will. The reason for this is that the dog firstly understands more clearly what you mean, the second is that if you go quickly at all, the chase instinct is aroused in the dog. That chase instinct, especially combined with a scared, screaming child, can illicit a prey response.
Anyway, just a few examples.
Again, I'm not a pit hater, or any other high energy or working dog breed. I do, however, feel very strongly about the needs of dogs who were bred to work. I'm not a trainer, but I have done a good deal of reading, and have owned 10 dogs, and been involved with several litters of puppies.