Understanding breed differences
Over the centuries dogs have been bred to suit all kinds of purposes, from companionship to guarding and hunting, and some of these traits will come out in their behaviour - it's not unusual to see collies trying to "herd" children, for instance! Working dogs have a strong drive to do what they were bred for, and need lots of exercise as an outlet for this or they may become bored and destructive.
As well as purebreds, there are crossbreeds and mongrels to consider when buying a dog. You shouldn't make your decision on looks alone - some cute and cuddly breeds can also be very demanding. Consider the breed's temperament, as well as its exercise needs, suitability as a pet and other needs it may have: some breeds have coats that require frequent grooming, for example.
The size of your dog can give an indication of its temperament and behaviour, although the breed itself is the best guideline:
Giant breeds: Giant dogs tend to be gentle and placid, but they need more space (eg in the car) and food than smaller breeds.
Large breeds: Large breeds are often lively and boisterous, although this means they may not be suitable for families with young children.
Medium breeds: Different breeds can have very different temperaments.
Small breeds: Smaller breeds tend to have been bred for small game hunting, so they can be noisy and energetic. Some have a tendency to nip which can make them unsuitable in households with small children.
Toy breeds: These dogs were bred for companionship, but this means they can be very needy and demand a lot of attention. Their fragility means may not be suitable for households with small children.
Purebred or mongrel: It's easier to predict the temperament and behaviour of purebreds, but you shouldn't assume every dog will act like its breed suggests! Purebreds can have a higher chance of developing genetic conditions, particularly as they get older, so it's important to be prepared for these.
It's often said that mongrels are healthier, longer-lived and gentler than purebreds, but this isn't necessarily true: all mongrels and purebreds are different and it's hard to predict how a puppy's personality will develop. It may be a good idea to get an adult mongrel rather than a puppy, as their temperament will be more established.
Coat type: Some coat types require more attention than others: smooth-coated dogs don't need much grooming, but long-haired breeds need to be brushed and combed daily. Breeds like poodles need to be clipped and bathed every six to eight weeks.
Dog or bitch: Dogs tend to grow larger than bitches, but behaviour is influenced much more than their training and environment than gender.