A good coin is a coin that has a high interest and price. and usually, they remain stable when the market situation decreases. and this is rarely encountered on any coins. but there are some coins like that.
A full research on their team, whitepaper,hard cap and soft cap if its attainable and if the project idea looks solid and promising plus if it have a physical product its a plus too. You just need time to examine and research the good coins to hold its on your own what you need or token that you will buy.