Part of deciding to add a dog to your family is making the choice between a puppy or an older dog. Each stage of a dog's life has numerous advantages to the other stages, so it really boils down to what matters to you most.
A Young Puppy: Nobody can resist a puppy; that sweet puppy smell, that adorabble face, and the insatiable curiosity. All cuteness aside though, puppies are a lot of work and every pleasure of a puppy has its match in unpleasantness.
The Teenaged Dog: From one to three years of age is, in my experience, the most frustrating period for dog owners. Like teenagers, they push their boundaries and try to get away with all sorts of mischeif. This is, unsurprisingly, the age that is most often surrendered to shelters by owners that can't take it anymore. Consistency and supervision are the most important things for this stage, even if it means going right back to basic puppy training.
A Fully-grown Adult Dog: From three to six years of age, a dog has really come into himself. He knows what feels good, what tastes good and where to get what he wants. Adult dogs know how to settle into the good life with little fuss.
A Senior Dog: Officially dogs are seniors by seven years of age, most dogs don't earn the "settled senior" title until they are nine years or older, especially smaller dogs that mature slower than larger breeds.