Some breeds of chickens are more dominant than other breeds. However most when raised together from chicks will get along. My Serama bantams get along very well. In fact if I raise roosters together and do not split them up, they continue to get along well after they get older. I just can't split up the Roos because if I do then it seems they will then find things to argue about afterwards.
I have some silkies and some d'uccles that hatched at the same time as a pair of Jersey Giant mix chicks that I have (which I now know are both pullets YAY!!!). They hatched together and were in the brooder together, and now they hang together 24/7. They are 3 months old now, and the JG mixes (one is black, one is blue, and the daddy of both is an EE so that's why they're mixes) seem to be blissfully unaware that they are bigger than the rest of their cohorts in the flock. And I mean, they are double the size of the bantams they live with! We have a decent sized yard, and we also have a large fowl mature flock. All the chickens live well together. We have silkies, d'uccles, bantam barnevelders, and a bantam cochin--life is all great and peaceful in the yard.
Well, it was until those two nasty cuckoo marans/BCM crosses got here... they're about to become kung pao and chile verde.