Thank you all for your input! I'm leaning towards Australorp, mainly because the birds I have now are really gentle, and I don't want to take the chance of getting a hen that could disrupt that. Perhaps if the flock was bigger, I wouldn't worry so much about that.
I will add 2 more chicks to my micro-micro-flock of 2 this spring. I currently have an Easter Egger and a Buff Orpington, which are both friendly, quiet, and generally easy-going, but don't really get along with each other. They are often found on opposite sides of the yard! I got them both as...