Best ROI GPU for ZCash Mining

hi guys,

i just tought about the best ROI gpu for mining zcash, and it seems second hand nVidia GTX 970 cards are the best. i just bought 1 for 170 dollars. its a fact that the 1060 6gb seems to be more efficient because less power consumation but you can get them way cheaper if you buy them second hand as the 1060 6GB or 1070 card.

what do you think about my thoughts? best choice or did i made a wrong calculation?

It highly depends of price, hashpowe, power usage,
for new cards you can check: