1080 ti`s are best for resale value, rx580 is the fastest roi. two mutually exclusive categories.
I doubt the 1080ti has better resale than say a 1060.
I think when gpu mining slows or dies out, hopefully the person had got ROI and is just looking to make a profit off the sale. Regardless, it seems like there is a lot of options but I'm looking for a rig that can perform and mine consistently for ayleast 6 months. With increasing difficulties I wonder if there 1060 can keep up.
I'm also leaning towards a 6 card system.