I will only recommend 3 altcoins that i think you can hold it safely for a long term,

1. ETH
2. ARPA
3. ADA

those three altcoins are going to be huge in the near future i think not everyone know a lot about those altcoins.
but still, i'm very confident that those coins are gonna skyrocket at least in the next 6 months.
that's what i'm hoping for.