When I started mining a couple of months ago I bought a 1070, it seemed to have the best ROI but I saw that a lot of people were using AMD cards and getting about the same hashrate, so I looked at AMD and I realised that the rx470 8GB was about £100 cheaper and decided to use the rx 470's due to the much faster ROI. At the moment I have a small rig (my first) that runs 4 x rx470 and my new rig that has 4 x 470s and 4 x 480s, my hash rate on the small rig is 110 and my new one on 7 cards is 184, all of the cards are bios modded but they still need to be undervolted and tweaked for performance. I've been working on it for days now, it's almost like having a full time job. : )