The 'best' breed for your flock depends on the reasons you have for keeping the flock - for meat and/or eggs, for poultry shows, for fun, or for 'enhancement of the beauty' of your farm. Most poultry species come in a variety of forms with differing production parameters.
A breed is defined as a group of related birds having the same general size, shape, and body form. All the birds within a given breed have the same skin color, number of toes, and plumage style. Most breeds have a number of varieties based on specific characteristics such as plumage color and pattern, feather placement or comb style.
Similarly, varieties can be furthered divided into strains. A strain is a related family of birds. For example, a flock developed and maintained by a specific breeder would be considered a strain.
Definition of the term 'breed' (American Livestock Breeds Conservancy)
Matching your need to the right breed: Chosing a bird for the home flocks (University of Maine)