On AMD Rx580 I have done some compare with claymore and for me on mono mining the winner is eminer: the reported share on the pool is very close to share reported from eminer.
I have two RX580 (GPU 1150MHz - memory 2175MHz), with eminer i go to 61.2Mh/s while with claymore I have 61.4Mh/s
On the pool the effective hashrate with eminer is from 57.8 to 59.8Mh/s (rarely also 60.1Mh/s!!!!) while with claymore is from 57 to only 58Mh/s ( )

I do not know why this happens but for now I prefer to use eminer!

Claymore has its merits in other peculiarities see the possibility of configuring Mhz and mV