I know that for printing some materials like the carbon-fiber filled PLA it's recommenced to use a steel nozzle since it'll wear-out a standard brass nozzle quickly. Is there any reason to prefer using a brass nozzle for 'simple' plastic-only filaments instead of just printing everything with steel?
Thermal conductivity of brass is approximately twice as better than steel (not stainless). Given that the size of nozzle is relatively small, it should be able to transfer enough heat for a medium-speed prints at least. I have printed PLA and ABS using "steel" nozzle (brand of steel unknown) at the speed around 80mm/s without any visible differences compared to brass.
However ideal nozzle I see as made of tempered bronze with polished inner channels. Bronze is known to have better friction coefficient and tempered one should be enough to resist carbon-type filaments more efficiently.