I prefer a mixed flock myself, that way you can see the personalities and behaviors of different breeds, the various feather colors are pretty and their eggs can be different colored too. There's an excellent article in the Learning Center on narrowing down your choices to best suit your needs:
https://www.backyardchickens.com/a/...cken-guide-to-picking-backyard-chicken-breeds
One important thing to keep in mind, individual chickens can vary within the breed. For example, just because a specific breed is known for their calm temperament does not guarantee that all the birds of that breed will act the same. They all have their individual personalities just as people do.
Good luck and have fun selecting your first flock!
