Looks like best investments were rx570 4gb 30mh for 250$5
Worst is nvidia 1070ti and 1080ti.  1.2k $ per card.  ROI is years and next gen is comming. thats make even harder to sell these hi end card at reasonable prices. while 1060 are good mh/s to wat. half of them startes dying because of dag file size today
should invest in pv solars also to reduce energy bill