To compare ,lets see the efficiency of 8 x GPU RX570 mining rig (average benchmarks 220mh/s at 1000 Watts, price 3000usd) :

• 4.55 watts per every mh/s
• price per mh/s 13.64 usd per every mh/s
• Currently Daily profit = 0.87usd after paying for power 0.11usd (06.09.2018)
• Currently ROI 2857 days

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Now lets see 8xGTX 1080 gpu mining rig ( average benchmarks 310 mh/s at 1100 Watts , price 5000 usd ) :

• 3.55 Watts per every mh/s
• price per mh/s 16.13 usd per every mh/s
• Currently Daily profit = 2.21usd after paying for power 0.11usd (06.09.2018)
• Currently ROI 2268 days

View post on imgur.com

Neither of these miners seems very profitable, GPU probably cannot handle even such long lifetime to make your investment back. All of this is of course as the mining profits has reached lowest point in a year.

But as we where looking for efficiency we have a winner which is Ethereum mining rig 310mh/s  

As mining profits as reached so low now that we cannot cove even the power costs, and if you want to run your mining rig as long as possible without  a loos you need to run efficient mining rig. Nvidia mining rigs can be quite expensive and if the mining profits would be slightly more best choise would be to choose Rx570 mining rig as it is much cheaper. Also another big factor is power cost if it is very low, less then most of the miners. I would go for RX570 mining rigs as your return would be much faster.

I know many people are mining at loos , this choice have to take yourself. Do you want to gamble or not.

See the video benchmarks on most efficient ethereum mining rig.