The most dangerous dogs are those that are not properly cared for, trained, socialized, housed, and fed. Breed makes little difference. I would have to say the pitbull because they can do the most damage, i know they are less aggressive than little dogs but if they bite you, you're pretty much screwed.
A dog is as dangerous as it learns to be. When treated poorly/abused, any dog will become mean & aggressive. The Presa Canario is HUGE & has the potential to be lethal if mistreated. The bigger the dog, the worse it is cared for, or trained to be mean, the more dangerous it is!
Dont listen to the fools who say its a Golden Retriever , They are really Amazing Dogs,Pitt Bulls Are good dogs to , but they ARE very protective , Rottweilers are mean , but still good dogs , It depends on how you treat them . But if your going to have a big , dog , make sure you give them enough to eat , because like us humans if they are hungry they become vicious. Hope it helps.