Chows -- now there's an unstable accident waiting to happen. I've read about more children being attacked by Chows than any other dog. Pit Bulls get a bad rap because *TADA* of the media exposure.
When I used to deliver home medical, I regularly stopped at a family who owned a very large Chow. It was vicious and once got through the door and bit me good - teeth breaking my skin. Being attacked by a dog is no fun - and these fucktards couldn't have cared less that I was bleeding

After that event, I always called the house ahead of time to have them meet me sans dog outside and needless to say they weren't happy. So if they didn't meet me out there, I just left the goddamn delivery in the middle of their driveway... dropped right out my car window. Screw you - your dog is never going to bite me again.
I blame the owners and not the dog. Chows, Pitbulls, and Dobes are beautiful animals. My ex-wife's family Doberman was the sweetest dog I've ever known.