I have raised both of these breeds and found them to be companionable if you take the time to acclimate them to handling as chicks. I have also had no problems with them with exhibiting aggression with other chickens/breeds or roosters. Their temperaments have been calm & docile.
With Yokohamas, I have had chicks fly out of the brooder to visit with me. The clients who bought them from me, tell me they are some of their calmest birds with sweet dispositions.
My first batch of Sumatras, were very attuned to me and remained calm when my activities brought me close to them, though were a mite jittery if I handled them. They were also fearful of my husband, and used to fly onto our roof if he was trying to corral them. He grew so frustrated by this that I sold them, even though I deeply admired their beauty and swagger. Their iridescence is stunning, and I love that the palms of their feet are yellow!
I now have a trio of frizzled Sumatras. One is "cuddly" friendly, follows me all about and seems to adore being held & petted; one is slightly skiddish; one is curious and seems to enjoy hanging out around me, but while she'll stay calm when picked up, does not appear to be thrilled by being handled. These three live in a flock of 48 chickens (14 breeds--some bantams- plenty of roosters), 20 ducks, 2 geese, and 14 guineas. They all get along; no rooster fights. These birds are now around 8 months old.
Haven't raised bantams of these breeds as yet, but I think the differences in temperaments would be pretty negligible. I would definitely recommend both breeds, but not to first time poultry keepers.
