so in case of ROI - vega 56 properly configured - now the best choice. because of crazy fast return on cryptonight coins
but it is very difficult to proper configure it and the rigs from vega works unstable.
so I agree with ixonite - choose gtx1070ti - it is more expensive then gtx1070 - like 5-8%, but you will receive more performance boost like 15-20% - which is nice.
and there is problem with nv card, just plug and mine!