It also depends on the memory size (4gb vs 8gb) of your RX 470/570. How so?
My rx 470 4gb cards hash at around 700-710 h/s while my rx 470 8GB cards hash around 770-780 h/s.

Although currently, because of the nice spike in Ethereum's price and based on whattomine.com, Ethereum is still the most profitable coin to mine with these cards.