Human-like personality traits I have noticed in dogs:
Boxers – these are essentially a mass-breed version of the English bulldog and were bred as such, for popular domestication in Britain. They are highly-intelligent and empathic and seem to have the most human-like personality of all dogs. They actually have teenage-like moods and can be sulky, and when upset will refuse commands and destroy carpets, curtains and pillows. They are also, alongside golden retrievers, the most benign of breeds, despite their potential predatory capacity (they have very powerful jaws and if you are actually attacked by a boxer - very rare, but can happen - you are in serious trouble). I have encountered boxers who bark a lot and might seem intimidating to people not used to such dogs, but I have never known of a 'dangerous' boxer (though I have no doubt there are some, they will be few in number). I recall one incident many years ago when a large boxer owned by a neighbour recognised me in the street and bounded towards me, almost knocking me over as it jumped-up wanting to play.
Rottweilers – originally bred by the Romans as a cattle dog, and became a hunting dog in the Middle Ages. Contrary to perhaps the popular perception, they are intelligent dogs, if trained correctly, but as a breed, they seem to have a Jekyll and Hyde personality. If they are trained early with a firm hand, they can be entirely benign, behaving much like golden retrievers, and in such circumstances they are very good with young children. On the other hand, if the early training goes wrong and their more primal, aggressive impulses are allowed to dominate, they become dangerous due to their instinct as both protectors and hunters.
Chihuahuas – a Mexican breed descended from a cross between a dog and a desert fox. This breed seems to be a bag of contradictions: very intelligent but very difficult to train (imagine a dog-like cat and you're close); very aggressive but also very affectionate. One defining characteristic of this breed is the tendency to form a bond with one person, who the chihuahua then jealously defends and can become possessive of. They can also be possessive of other pets you have that they are used to: especially cats, with whom they will form a bond and will be jealous and aggressive towards anybody who touches the other pet. They also have a protective instinct and will follow and kneel and walk near their owner, always on the look-out for threats and will sometimes bark and growl, and even lunge at, anybody who comes near the owner. Furthermore, they also have a strong possessory instinct which extends to any item of property they identify as theirs, whether it is a chair, a bag, a book or whatever, and will growl and lunge at you if you touch the item they identify as theirs. Chihuahuas suffer from a 'small dog complex' and hardly-ever get on with other dogs and other small domestic animals like cats that are not yours, and will constantly bark on seeing a strange dog or cat. They should not be allowed unsupervised near young children, even if they seem well-behaved and obedient: a trained chihuahua is perhaps more of a risk than a trained rottweiler, as the chihuahua has an unpredictable element to its personality and due to its smallness in size, is very defensive and can lash out.