Guard dogs are purpose-bred, so that ticks one of my two boxes for extra caution. Some hunting breeds also raise my level of awareness, as a few aren't bred to interact as pets.
Small over-bred and recklessly-bred varieties, like Chihuahuas, are perhaps the worst biters of all. Their transgressions just aren't serious enough to make headlines. I've only been bitten by two dogs, and both were lap-size breeds.
The thing to remember about dogs is dogs are
dogs before they are a particular breed. Their instincts have more to do with being a dog than with being a particular breed.
And the dog species is that of a social animal, who is also a predator, who also has loyalty towards his particular pack, and sometimes territorialism towards members of a different pack.
So a dogs behavior toward you will depend on which of those instincts is turned on with regards to you: social instinct, or predatory, or territorial, or bonded pack member.
And the question of which of those instincts is more likely to be turned on has mostly to do with the conditioning the dog has been through, its background and experiences, the amount of exercise it has (under-exercised dogs are more likely to have behavior problems) whether its owner is the leader or the dog is the leader (a dog who is the leader will be more likely to take the initiative to go into a hunting mode or a protective mode, a dog who is submissive to his owner is safer), the emotional energy the dog picks up on from humans, etc. Particular breeds do have more
capacity, more
potential, for being good at following a particular instinct. But whether or not that particular instinct is actually turned on in regards to humans or different one is, is something that can be controlled by humans (this is usually an unconscious process on the part of most humans-it sometimes goes badly because people often don't know what they're doing). And in the case of a particular dog at a particular given moment, it can be judged more accurately by body language than by anything else. Unfortunately, most people can't read dog body language.