I know gray hatch game hens are very good mothers. I have had some gray hatch X Leghorns that are excellent mothers as well. Very protective of their chicks I've seen them attack our dogs and my pigs.
Silkies are good broodies as well, and I have seen light Sussex that were very persistent sitters.
I keep thinking to natural incubation/brooding. I haven't had any luck with hens that will commit. I have and still consider getting some birds for this reason.