which is the most dangerous breed of dogs ?

A pissed off one.

Any dog that is breed to attack and be aggressive when the owner is not capable of controlling the animal.(I'm not talking about police/corrections dogs either)

depends how they are brought up staffys are dangerous if brought up by the wrong people and that applys to most dogs

The pit bull is frequently the target of that title. While not technically a breed, “pit bull” is a term typically used to categorize breeds which were once associated with bull baiting and pit fighting , including the American Pit Bull Terrier, American Staffordshire Terrier and the Staffordshire Bull Terrier.

Rottweilers and other dogs that have been bred for their aggression.

Either a Rottweiler, Doberman, Bulldog, or Chow.

The greyhound I believe. They are too fast and they have really sharp teeth and are naturally vicious.

any dog, regardless of size, that is taught to show aggression can be dangerous.

People say Rottweilers and Pit Bulls, but I've also seen Rotties and Pit Bulls that are very gentle and sweet. I'd say that any dog that is properly trained and treated well will be a good dog. Dogs that spend too much time in a pet store before being purchased (therefore unsocialized), and dogs at a shelter who have been mistreated and lack trust would be more dangerous. Not to say that these dogs cannot be helped. My dog spent his first four months of life in a cage in a pet store. Then he tried to bite two people, and since then, we've spent probably $1000 or more on training (some private lessons, some class lessons once he could be trusted around other people and their dogs) to try and fix him. He's doing better, but it is a lot of work, and even now, we have to watch every move he makes because we never know if he could regress.