For availability, the 970 comes out on top. Cryptocurrency miners are gobbling up 1060s (the 6GB models, not the crippled in comparison 3GB models) almost as fast as they are comparable AMD offerings. If you can find a 1060 6GB at a reasonable price AND in stock, grab it over the 970. It doesn't have the RAM limitation issues of the 970 and is better overall.
EDIT: I should clarify. the 1060 isn't significantly better than a 970, and the difference wouldn't be worth an upgrade to a 1060 from a 970 for performance alone. It is still, an improvement though.