Ethereum is no doubt that 2nd most valuable cryptocurrency after Bitcoin but mining of Ethereum has reached to point of being not profitable anymore.
The most energy efficient GPUs used for mining are currently right now. AMD RX-480, RX-580. On stock configuration, these GPUs are giving per day return of approx 1.7$ only.
Mining of Altcoins is not primary objective of miners right now, but after Bitcoin & Ethereum, there is gonna be major shift towards other coins. I am sharing some potential cryoptocurrencies which could return handsome profit with reference to above mentioned GPUs.
Monero (XMR)
Monero has true potential to retain its position in top 10 coins alongwith more value in future. Right now its difficulty is not so much less but it can be a good option to mine this coin. Right now its giving approx. 1.2 $ but its value can increase in future, so after Ethereum, the most sought coin for mining would be Monero.ByteCoin (BCN)
Bytecoin is another cryptonight coin, whose value can increase in future. Right now its giving approx 1.07 $ .Ethereum dual mining
Although Ethereum is not feasible anymore, but for time being some survival can be done by dual mining with it. Some good coins to mine with Ethereum are Lbry, Decreed & Siacoin. Lbry & Siacoin can become more valuable in future. There pairs are right now giving approx ETH/Lbry= 2.1$, ETH/Siacoin= 2.7$, ETH/DCR= 2.2$Monero dual mining
Monero can also be mined along-with other coins and together they can provide good profitable result in few months. Some coins which can be mined with Monero are XDN, FCN etc.