I have three hens, a BO, BR, and a Black Star (Black sex-link)
Numi the black star lays almost every day. She likes to take saturdays off though.
She is sweet and curious, she runs up to me for petting, and will perch on my arm. I think she is also the smartest (that is a relative term) as she seems to understand a situation more quickly and calms down faster. She does have a hard time finding a place to lay, she made herself a grass nest in the yard, and wants out of the coop everyday to go lay in it.
Ella, my Barred rock is a typical middle child. She lays an egg every other day, and is quiet and sweet. She is the easiest to carry around.
Gillian the Buff Orpington is the silliest. She adores dust bathing, and does it often with much glee. She usually lays an egg a day, but takes days off more often than Numi. She squawks the most when she lays eggs, but I guess she has reason to, they are the biggest. She really doesn't like being carried, but loves scratches and pets.
All my girls REALLY love coming inside, and if they had their way, they would be house chickens with a chicken door.
Here are a couple of my reasons for getting different kinds of chickens.
1) I am able to tell their eggs apart. I like knowing who laid when and how often. If they were all the same breed, I might not be able to tell.
2)Numi will lay the most during the spring, summer and fall, but Ella and Gillian will lay through the winter.
3) Gillian is easy to see when it's dark. Since they all stick together, I can tell where they are without going out and searching in the dark for dark chickens. However, the dark coloring might keep the others safer from predators.
4) Ella and Gillian seem to handle the heat easier. Numi, being black, pants and fluffs her wings the most.
They don't peck at each other, and they prefer to be within a few feet of each other. I did get them all at the same age and they do have a LOT of room.