Ethereum is a very good choice for long-term investment, it is fairly safe to invest in Ethereum because most of the new projects are launched in Ethereum blockchain. And its developer Vitalik Buterin is a very talented and challenging person. I think Vitalik will do his best to keep Ethereum alive. so I think the price of Ethereum will increase significantly in the next 5 years.
Ethereum's been one of the best-performing cryptocurrencies on the market. It would be hard to ignore it, especially when it's the leading smart contract platform in the world. With Vitalik behind it, the project would be on a road towards non-stop success. I wouldn't say the same for other altcoins, simply because they're fairly new to the crypto/Blockchain space. Their blockchain networks are not as tried-and-tested as Ethereum's which means they're easily subject to failure.
Many people believe Solana to be a good investment, but network performance tells us otherwise. It's been subject to several network disruptions, putting the project's reliability claims at risk. There's been talks about introducing an "observation system" in order to "better identify issues and patch them accordingly". If the Solana team does this, the network will effectively become centralized.
That's why choosing altcoins which prioritize decentralization should be on the top of your list. We can never know what'll happen 5 years from now since crypto behaves in many strange and bizarre ways. As long as you make your decisions based on research (not someone else's opinion), you can rest assured your investment will last for a very long time. Just my thoughts