Choose your dog according to what it was bred to do
"Finding the perfect pet: If you choose your dog for its personality -- not just its looks -- you're barking up the right tree" suggests that:
The key to finding the right dog for your particular lifestyle is looking back at a breed's original function and understanding how its ingrained temperament translates in today's world. Vizslas were bred to be active companions to Hungarian hunters; they'll go stir-crazy without running a few miles each day. Keeshonds alerted captains of Dutch barges; if a leaf blows by in the yard, you'll be informed. Neopolitan mastiffs, sort of dogdom's living gargoyle, kept strangers out of Italian courtyards by sheer looks; if a guest comes in uninvited, they will not benignly point the way to the silverware.
Before you choose a breed of puppy, ask lots of questions of the breeder, and do a little research. Find out what the breed's primary traits are. You'll be living with those traits a long time.