Some may be reserved with strangers unless very well socialized as puppies. These dogs are watchdogs, not guard dogs, although some have been known to guard. They can become destructive if left too much to their own devices. Train Labradors early not to pull on the leash, as they have very strong necks. Show lines are generally heavier and easier going than field lines.
Field lines tend to be very energetic and high strung.
This breed is very popular. If you are planning to show, buy only from a reputable breeder. Labs are a bit more dominant and independent than the Golden Retriever.