i used to do a lot of house delivery calls for a family water business we had years ago. id go into a lot of different homes with a lot of different animals. ive never once felt threatened by a pit, or a rott, or a dog that typically has the bad guy image attached to it. i have been bitten by poodles and by yorkie terriers and by pomeranians. i hate those little bastards.
i think its much more to do with the owner. most owners think its cute to have a tiny dog act aggressive. its all fun and smiles until a delivery man get bitten through jean, behind the knee. and trust me, im a huge animal lover, but ive never wanted to punt anything harder than when that yorkie's teeth sank into that soft spot on the backside of my leg. pitt owners, and boxer owners, and rott owners are much more respectful of the dogs and the dangers they pose to people if the wrong behaviors are reinforced. toy dog owners, not so much.