If I were you, I'd likely go with the 1070, as it will likely give you the most longevity, and since that's what you're looking for. It's not significantly more expensive than a 1060, and the benchmarks that I looked at seem to show that it's a good investment.
At the end of the day, either card in the 10 series will get you what you're looking for. Mostly your choice will probably depend on what resolution you play at. If you play at 1080p, I'd roll with GTX1060, if you use 1440p, I'd go GTX1070. Right now, for me personally, I use 2 980TIs right now at 2560x1440, and I have absolutely zero complaints other than SLI Stability, so I can only imagine the 1060/70 will be that much better.
Edit: Here are the benchmark graphs I used, if you're particularly interested:
http://bit.ly/2ccmv5b