1070 have more option for sure, with amd you are stuck there mining ETH,if ethereum sink what you will do with amd gpu? nothing, there is only monero which is not profitable, other algo are not optimized or the optimization is private
Care to elaborate on that part ?
hasn't AMD been the best brand overall for mining over the past years, and not just for ETH (I'm thinking aboute BTC of course, Litecoin, BOINC etc... ) ?
Sure. But that's in the past before nVidia Pascal came to the market a year ago. nVidia Pascal architecture is way more energy efficient than Polaris when the GPU core is heavily utilized. If there's a good CUDA optimized miner for a certain algo, a GTX 1070 murders a Polaris with hashrate and efficiency. And of course it should since it's a more advanced and more expensive card.
BTW, mining with Polaris cards is an absolute pain in the ass with the need for bios mods to get a decent hashrate, many different memory brands which need different individual bios tweaks, the need for hdmi dummy plugs or monitors connected to the cards, tweaking with wattool, etc.