The Penedesenca is unique in that no other breed can produce eggs as dark as they can. They also make great meat birds, but their unrecognized status makes them difficult to act as show birds.
The Phoenix breed is famous for its incredibly long tail, making them wonderful in the show circuit. They aren't, however, very good at anything else and do require a lot of care to keep their tails undamaged.
Plymouth Rocks may just be the most popular breed in the US due to theri excellent egg laying and hearty frames that make for a good meal. They're also easy to tame and non-aggresive. What's not to like?
The Polish breed is best known for their magnificent V-shaped crest, making them great as show birds. They also have a decent egg laying ability, though this isn't as reliable as other breeds.