Undoubtedly ETH is the one I am looking out for because of many Dapps, interoperability and the pioneer of all smart contracts.
To me, this is the best long term altcoin up to date and worth to DCA (dollar-cost averaging) while Bitcoin is still the king.
Other altcoins than ETH they are just good for either short or mid-term investments.
I think when talking Ethereum no one doubts it and this is the best altcoin,
for long-term investment Ethereum is indeed one of the best options because it is feasible and safe,
it's clear that it will be profitable.