PoW coins that's relatively low in traffic, newly created with low amount of miners or PoS coins. elon's view regarding energy consumption feels so random though, he prefer coin that's green but choose doge instead even though there's other coins that are greener and better. however, Nano have been discussed a lot recently and people keep saying that it's greener than doge by a lot so maybe nano is the good option here if we're talking about low energy consumption.
You got that right, but I think POW is an outdated system of mining, POS coins would have been much more better since it doesn't requires energy to mine instead it's mining power is based on the amount of coin held, so a POS coin would have been better and there are many out there which got great potentials, talking about Elon Musk! He is a business man and would do anything which will go in it's favour in order to move his business forward and push his name to the top.