I believe all dogs are different regardless of their breed. Breed provides a basic characteristic that is obsevered in most dogs of the breed. For example, Labrador Retriever. They were used by fishermen for retrieving fish that got out of the net etc and thus they require a lot of exercise and are high energy. But within the Breed, I've seen and owned many many dogs that are extremely lazy. I've owned many Labs and not all have been as friendly and as sociable as what Labs are usually known for. One of my Labs is pretty independent and another one extremely snuggly. A dog from a responsible breeder can be calm, well socialised and even tempered because s/he is provided with all the necessary training from the mother, owner and litter mates. In a shelter the dog's or the pup's history is unknown. S/he could have been separated from the litter and the mother at a very early age and thus not been properly socialised. The dog's personality largely depends on what s/he has been through and is. If you want a dog that is exactly suitable to your needs, you can observe it's nature and temperament at the shelter and then select one accordingly.