I joined crypto in 2017 and until now I still find it difficult to find or choose which project I should hold for a long time and it is true that the safest point is to keep your assets in the top 20 coinmarketcap, at least the project already has a very clear roadmap and team.
If you want to invest long-term in this market, you should only buy the top altcoins in the market such as ETH, BNB, XLM, TRX, NEO .. and Bitcoin. Those are the best projects and their price will always grow in the long run, don't waste time on new projects because in the long run its price can crash many times or die any time