The domestic dog, or Canis familiaris, has 78 chromosomes — the same number as a wolf. Whether the dog is a chihuahua or an Irish wolfhound the number of chromosomes is still the same, thus, there is no difference between breeds of dogs and the ancient bedrock of behaviour stemming from the wolf. Qualitatively speaking, genetic manipulation has virtually no effect on behaviour due to the intense genetic selection.
You can breed selectively for a dog that brings back more food to the pack, or to guard the den more effectively, but we can't teach them abstract thought or conditional sentences — "if you do that again I'll be very angry", will only ever be a tone of voice or a body gesture to a dog, nothing more.
Dogs, whatever the breed, all have excellent cognitive powers, are amazingly perceptive to nuance and observe the most imperceptible changes within us.
On saying that, different breeds have different stamina, sensory perceptions, size, agility and emotions. These are the differences that one will need to take into account when bringing a new dog into the home.
Which Breed to bring back to your home?
Take an honest look at your life. Don't fall for the cutest face or biggest round set of eyes, because the puppy you chose for life, to honour, love and cherish will become a dog that may need special requirements and certain commitments.
Are you a couch potato? Some dogs will need more exercise than others eg Pointer needs more than a Pug, and Galgos make excellent companion couch potatoes!
Some will need high maintenance grooming to keep healthy coat and mind, e.g. Spaniels or Shih Tzu compared to a mini pinscher.
Do you have a spare 1000 euros, dollars or pounds? Some breeds will have significantly shorter lifespan and will therefore incur medical costs associated with old age that much sooner, e.g. Great Danes.
Other breeds come with genetic characteristics that may require extra veterinary care. For example, the bulldog intolerant of hot weather may easily die in the heat through breathing difficulties and is subject to many genetic health problems costing thousands to treat.
Do you live in a one bedroom flat, have a house with a garden or own a farm? Size is important, big dogs need room (or a huge couch) to grow and stretch. Compare a wolfhound to a maltese.
Do you have children? Human children are seen by a dogs as a very different species to a human adult. Children walk differently, maintain eye contact, make more noise and have a tendency to tug and pull. It is important to find a breed that is generally known to be calm and tolerant and then teach your children the correct behaviour around dogs. Maltese, for example, are not considered good breeds for children whereas the Cavalier King Charles generally love kids, according to the AKBA.
If you are looking for a specific breed, the ABKA has a wonderful informative breed dictionary. I also strongly recommend that you look for breeders that abide by the code of ethics for specific breeds. For example, German Shepherds suffer from hip dysplasia and will suffer extreme pain as their hips start to collapse, causing massive veterinary bills and unnecessary discomfort. Many of you may have noticed German Shepherds on the streets of Barcelona with very poor hip scoring. It is very important to look for reputable breeders.