There's been a quite a lot of this sort of discussion, and if you check similar threads here you'll see a range of opinions. I think it depends on your risk tolerance. If you have to go 1070 for some reason, personally I prefer the 1070ti since the extra CUDAs have a real impact for only slightly more price.

Overall just  depends on how much capital you can afford tie up in equipment, your risk tolerance, belief in the future crypto, what you want to mine and whether it will be asic'ed or fpga'ed (some believe everything will) and whether makes sense for you to  just wait for the 11 series cards dropping soon. Good luck.