What actually is an investment? In simple terms, it is when you invest in a project with the view of getting a return or profit after a certain number of days, weeks or as the case may be. Now since Tether or Gemini USD is stable, how then is it an investment?
Yes, it is not volatile but if you are looking for a coin which will give you return then stablecoins are not an option, but if you want to Hegde your assets against volatility, then stablecoins are the right choice, which is why during a bear market people move to stablecoins and when the market changes (bull market) they move to their preferred coins.

Now to air my view about investing in crypto while having in mind that crypto is volatile, I would prefer investing in Bitcoin because it is the best till date. Even when it drops owing to bear market, it is also the first to move during a bull market. Another coin which is better is Ethereum and most major coins. But as for newer altcoins, a good number of them will dump and never rise again, or dump and never attain a good price ever again; so that still brings us to the best choice, Bitcoin.