Well, I can recommend to invest in ethereum and litecoin. Both altcoins have a high potential for high return. In my opinion this is low-risk investments.
I agree with you that the two altcoins between ethereum and litecoin are very good to invest but after all it depends on each of you
Litecoin is undervalued because people are just talking too much about bitcoin and ETH.
If we look at the price history of Litecoin, it also rise to the occasion like when there is a bull run, therefore I would also invest with litecoin
if I have to choose among the altcoins. However, I would not only invest in 2, I'd rather diversify my investment for proper risk management.