If you are seeking for a long term cryptocurrency better to do your own research. We can recommend good coins but you still have to study it. I suggest NEO, Ethereum, Cardano, Monero and Litecoin if you want a long term altcoins. You also need to accumulate bitcoin as well because it is the main coin of all.
Yeah, correct this is all just a suggestion you still need to study the coins first to see if it will fit your needs. Some coins take time to increase, some of them have big pumps and dumps it is up to you.