Welcome to BYC. Glad you decided to join our flock. I've had all three of those breeds over the years and they are all three great breeds. I slightly prefer the Black Australorps to the other two breeds as they are the most heat hardy (all three breeds are very cold hardy) and the best layers of the three. All three breeds are generally docile, and Australorps and Orpingtons are especially calm and gentle birds. Our children and granddaughter (pictured in my avatar) all made lap pets of both our Australorps and Orpingtons. As NorthFlChick said, there is no reason why you can't keep all three breeds together in a flock. Please feel free to ask any questions you may have. We are here to help in any way we can. Whatever breed you decide to get, good luck with your flock.