as i said AT THE MOMENT OF WRITING , stongest card providing HIGHER HASH RATE (no matter the power consumption) is RADEON PRO DUO ... 900 to 1100 hashes /s depending on the oc you apply ... of course the higher the hash rates the more inefficient it is... at 900 hashes is a bit less efficient than nvidia cards (4.5 w for each hash)
Out of production for at least a couple months, try FINDING one at all much less at a reasonable price.
Nice if you CAN find one though.
To crazyivan - I'm not the one with the MSI 1070 cards, mine are all Gigabyte or EVGA and at this time I don't worry about "optimise for sol/s" as I'm on a "fixed price for electric usage" lease.
(That should change VERY shortly though).