My experience is the following:

For ETH, the GTX 1060 3GB seems to be the best. I get 24MH/S for 75-80W (for around 200$) while with a 1070 I get 32MH/S for 90W (for around 400$).
Now if you want to mine ZEC for example, the result will be different, a 1080TI would probably be a better option.