I think Artix-7 would be the best one/most cost efficient to mine BTC on, Virtex is a bit of overkill, and a lot more expensive.
Zynq would probably be amazing as well though (I think)
It seems to be a lot harder to get bitcoin miners to place and route successfully on Artix-7 than on Kintex-7.
I just updated the repo with a DSP48E1 design, for Kintex 7. 400MH/s using 80% of the DSPs, and ~25% of random logic. I don't have an Artix-7 to port to, but I think they also have DSP48E1's. I plan to start revamping the code base to better support multi-core designs and standardize the communication modules. Hope to get my Kintex up to at least 1GH/s by throwing in two regular hashing cores.
Cool!