Hodl, or long-term investment, is ideal for earning with bitcoin. Also, as such a coin, you can still consider Ethereum. As for the other coins, absolutely not all of them are promising, so it is better to use a trading strategy for them.
Yes, if now you decide which of the cryptocurrencies is the best one for hodling, it will be Ethereum. Its price can stay very low for long, but in 1-2 years this altcoin will gain a lot.