German Shepherds do not have the best sense of smell. They do have an exceptionally good sense of smell and that is one reason they are used for police work. However breeds like the Blood Hound have much more precise smell.
It is said that the bear has the best sense of smell of any animal. A bloodhound has an excellent sense of smell at 300 times better than that of human's. A bear's sense of smell is seven times better than that of a bloodhound.
Beagles have a better sense of smell than a German shepherd. Beagles have the second best sense of smell out of all the dog breeds. The only dog with a better sense of smell than a beagle is a blood hound.