I would like to get the 1080ti but I would then need to also upgrade my PSU which is a cost I probably cannot afford so I think im going to go for the 1070 because I can purchase it sooner and just plug it in and go. I am going to check out the AMD side like someone suggested first though.
I have a 1080ti rig and from my experience so far my 1070 rigs are better value for the money.