Here is some great info on chicken breeds from Wikipedia. Couldn’t say it better myself, so here you go.
There are literally hundreds of chicken breeds in existence. Domesticated for thousands of years, distinguishable breeds of chicken have been present since the combined factors of geographical isolation and selection for desired characteristics created regional types with distinct physical and behavioral traits passed on to their offspring.
The physical traits used to distinguish chicken breeds are size, plumage color, comb type, skin color, number of toes, amount of feathering, earlobe color, egg color, and place of origin. They are also roughly divided by primary use, whether for eggs, meat, or ornamental purposes, and with some considered to be dual-purpose.
In the 21st century, chickens are frequently bred according to predetermined breed standards set down by governing organizations. The most commonly used of such standards is the Standard of Perfection published by the American Poultry Association (APA), the oldest livestock organization in the New World.
Others include European standards (especially British ones), and that of the American Bantam Association, which deals exclusively with bantam fowl. Only some of the known breeds are included in these publications, and only those breeds are eligible to be shown competitively.
There are additionally a few hybrid strains which are common in the poultry world, especially in large poultry farms. These types are first generation crosses of true breeds. Hybrids do not reliably pass on their features to their offspring, but are highly valued for their producing abilities.
Finding the chicken breed that works for you is so important. We are going through that process right now. Trying several breeds to see what personality we like. What body type and egg size and color we think is best, etc. What we are finding out is that each chicken is unique and we are having a blast with our chicken breed research.
Photo is of a beautiful Splash Wyandotte Rooster we just got from Debra Turnell. Thanks, Debra.