Bitcoin mining would work better on the R9 295x2, but it pretty much isn't worthwhile mining on GPUs anymore, hasn't been since the initial mining craze back in late 2013 early 2014. I'd say the 1070 would be the better buy, you'd get better performance in games where Crossfire doesn't work, roughly similar performance in games where Crossfire does work, while also having a much cooler running and power efficient GPU.