Small new coins may have the best ROI for your rigs, if, and only if that coin goes up in value.
You can stick with main coins and earn some money, or you can take the risk and mine new emerging coins.
For example i have mined ITNS in the beginning, i still do mine it despite ETH/zcash being more profitable to mine for me atm, but i believe in the coin. Coin went x10-x20 in price since i have started to mine it so i hade a lot of profit much much more than i did mining ETH/zcash.
But the coin went up in value. if it did not go up i would end up with less money
i have tried monero / ETN / DCY / Bitcoal / XLC / Bib .. etc most of cryptonight ... since i my GPU is gtx 1050 and use my processor too ..
i move from coin to coin to get profit .. and sometimes i store somecoins for future " like storing bitcoal and xlc " it jumped from .05 to .3 to .5 now ))
also coins like DCY it's price was .005 and i could mine 1500 coins or more easily per day .. which makes me more profit than i could have from monero in 6 days.
also i found Dero in my way .. the price goes up from .7 to 1.8 .. and i can mine 73 coins perday " with my friend helps sure" that's make it worthy .. if the price stays at this value sure.