Yes, bitcoin is a time-tested coin that has shown record price growth for investing in such a short period of time since its creation. But among altcoins, there is, in my opinion, the same reliable coin, and this coin is ETH.
ETH can be considered a coin worth investing in, mostly the top 10 from any coin aggregator website falls in the "good to invest" category but must invest is bitcoin.
So for stock markets, indeed I have experience in that prior to bitcoin, I actively do buy stocks from companies that I fell are going to do well. It has its ups and downs but all part of the game and it is a good diversification beyond crypto.
Never diversify into altcoins, they are almost useless. But traditional assets will be always an option to put your money on.