Briefly put below is a short explanation of the different types of Labradors along with a few pictures.
ENGLISH / CONFORMATION TYPE
English Labs have a squarer head and a thicker muzzle. They have a strong powerful neck that blends nicely into the shoulders,they are heavier boned than the "American Labs" and have nice thick otter tails.Their coat is a double one, a soft undercoat with a harsher outer coat. They are very close to the breed standard per AKC. They are the type of Labs that you usually see in the show ring. English Labs tend to be calm natured and of lower energy level.
AMERICAN / FIELD TRIAL TYPE
American Labs tend to be smaller boned, with longer slimer legs. Their heads tend to be narrow and more rounded and their muzzles longer, their tail is longer and thinner than the English Lab. They often don't have the proper double coat. American Labs are judged for competition in the field, they are not judged on appearance like the English labs but soley on performance. They are great for hunters and they have plenty of energy and can go all day.
Often the use of American or Field type is not appropriate and actually those dogs being discribed are in fact in reality "poor quality". True "Field Labradors" are owned and bred by people with a goal in mind!! The poor quality Labs are most often reproduced by folks with little to no knowledge of the breed standard and are usually only interested in the money to be made from puppy production.
Regardless of the "look" any dog used for breeding should have proved itself in either the Show or Obedience ring or have been sucessful at Hunt Tests or Field Trials. Clearances for hips, elbows and eyes are extremly important also prior to be adding to any breeding program.