For long-term investments, I recommend that bitcoin or ethereum are the best choices because seeing the market prices of these two digital currencies in recent years have experienced significant market price changes, and if you are afraid of losing a lot of your money then I suggest you invest in only gold because it is very certain to get a profit in the future.
Bitcoin is the safest currency to incest if you are dealing long term though there are some coins that is also supported by the business in crypto like Binance (BNB) in which surely will be the best option unless they turned out being scam in the future(things that i doubt will happen)
invest only in currency that you can be sure to be safest because we knew how market in crypto moves , this is like a roller coaster and also a very risky investing place.