I have 3 of each in my flock of 8. They mingle nicely. Top hen is a bossy Barred Rock but the lower ranks are a balance of the rest. Lowest bird is a Barred Rock. They all roost side by side with no more squabbles between birds of different breeds than between birds of the same breed. Many times the line up on the roost is Barred Rock, Buff Orpington, Barred Rock, Buff Orpington, etc.
I got the Buffs as chicks first and the Rock chicks about 5 weeks later. Integration of the younger Rocks went well. Had it been the other way around and the Buffs been the younger birds, I think the Rocks would have given them a hard time.