Since nothing has been posted here many months now, I would like to input some as I am going to build a rig. I am currently on the researching mode and here are some amd based gpu that I found to be worth it or in available supply (rx470 or rx480 are hard to find in brand new condition these days):
rx570 8gb
rx580 8gb
rx vega 56
rx vega 64
Of all listed above, my choice for a mining rig would be the rx570. That's because the the price is lower while its hashing power is not that far behind with the rx580. rx vega series is nice to have, but the price is too much for me. But if you have the money, the vegas are the best choice.
For the motherboad, my choice would be Gigabyte GA-H110-D3A since it is designed for mining with 6 gpu. Plus the price is affordable.
Nowadays, if you have the money, the rx vega series are very good choice. On the other side of this hardware competition, I think the gtx1070, gtx1070ti, gtx1080, gtx1080ti, p104-100, p102 are the only best choice.
By the way, I compute profitability using this calculator
https://crypt0.zone/calculator . I hope you'll find this one convenient too.
And now: I believe this is all beautiful if you got very cheap or free electricity though.
