Different breeds also have different needs. So do families. You need to honestly ask yourself how much time you have for a dog. How big is your garden? How much time do you have to spend with your dog? Will you have time to walk them regularly? Have them trained? Do you have very small children in the house? What will you do with the dog if you go away on vacation often?
If you are sure you want a dog you need to think very carefully about what kind of breed will suit your family's needs. What kinds of things should you look for when choosing a breed and buying the dog?
You should try to find out more about the breed before you get the dog. Try to read whatever you can about the breed you are thinking about choosing. It's really vital that you learn as much as you can about the breed you are intending to buy. Some dogs are more susceptible to different genetic disorders.
Large dogs can suffer all kinds of problems. Their joints and bones are vulnerable. They are more susceptible to hip-displasia - a degenerative hip disease which can be painful and chronic. They take up much more room so you will need a large back yard for them to run; they need lots of exercise. If you are on a tighter budge you may want to consider a smaller dog because they do not eat as much.
Smaller breeds have problems of their own. Little dogs with short noses (muzzles) are susceptible to breathing problems far more than their larger counterparts. This is because there is not as much space for the breathing organs to develop. You can't tell by looking at a puppy, whether they will have health problems later in life. Smaller breeds are prone to sinus and nasal problems. There are many other breeds with specific health risks associated.
Grooming should be another consideration before you buy a dog. If you have the time to come your new Yorkshire Terrier or Maltese then by all means get this breed. They require daily combing of the hair however you can keep it short. The more self sufficient breeds would be the Boston Terrier or Pugs. They have such short hair that it needs very little maintenance.
Ask dog breeders any questions before deciding and buying the dog. A professional dog breeder can tell you more about the specifics on the particular breed you are considering.