Yesterday, I was looking at m.2 drives when I noticed a GTX 1060 costs $500. Then I kinda assumed it was due to a spike in mining and researched it a bit and couldn't believe it. Micro Center had 64 GPU's in stock lol. Mostly low end ones. So, my 2 MSI EK Hawk 1070's were $350 ea. and I saw closed auctions on eBay for over $500 used.
Kinda was thinking about selling them lol. But, I wouldn't be able to buy any after I did. Then I thought I should mine, watched 1 video, and got frustrated by how advanced the whole process is.
Anyway, long story short, yes GPU's are the best to fold on in terms of PPD per watt ratios by far.