The RX470 by Sapphire is the best 470 on the market due to their selection of RAM, they are the only 470 manufacture that uses the same RAM chips (the 8GB version) that are in the RX480 models giving you a higher through put. Right now it's +1 for these cards if you are doing traditional GPU mining. As a comparison here are some numbers
RX480 Reference Board - ~27MH Etherum
RX470 8GB Sapphire Board - ~25MH Etherum
RX470 Everyone elase - 23MH or Less
-IceBurst