Why do you want a sheepdog?
As stated, Sheepdogs are among the smartest groups of dog breeds. They are very active and alert, which is why they are decent guard dogs.
However, beyond anything else, Shepherd Dogs are very loyal to their families and provide excellent companionship due to the long and historic relationships these breeds have had with humans for centuries.
It would probably be hard to find a more loyal, loving dog, but make sure you can keep up with him!