Any breed of dog can be the 'most' aggressive - but there are some that are labeled as most aggressive - among them pit bulls, my favorite breed malamute, and huskies, northern breeds in general. However, I have to add the qualifier here that it is all about how these dogs are raised and what people do to train them that makes the total difference. If you look up which dogs are not good with families or social situations, you will find the breeds above and then some. However, if you train ANY dog the correct way and socialize them, I am of the firm belief that they do not need to display that aggression. You also must of course not put them in situations that CAUSE aggression.