If you go the shelter route, then you're going to have your choice of what's there. This means a broad range of breeds, shapes and sizes of all ages to choose from. Do your homework before you get there to help you narrow down your selection.
It can be tough to get an accurate reading of a dog's energy when they're in a cage. Ask if you can take the dog out into a larger area or even take the dog on a short walk. Once you get the pooch away from other dogs, you'll get a better sense of their personality.
Renowned dog trainer Cesar "The Dog Whisperer" Millan recommends asking the shelter employees about temperament and disposition. His feeling is that the shelter worker is most concerned about making the right match. He also recommends checking your emotions at the door and not letting the circumstance of a particular dog outweigh finding the best match for your family.