I prefer to hold large amounts of coins on a Cold wallet because I know how to create a cold wallet safely, how to back up seed phrases and store them in a secure way. In overall, I know how to keep my cold wallet safe. For a person like me, it's better to use cold wallet instead of online exchange. If you are a person who doesn't know how to create and use cold wallet, how to keep seed phrases safely and other details, then it's better to use online exchange. Many will argue with me cold wallet is better but in this case when person doesn't know how to create a cold wallet and how to keep Bitcoins safely, such a person will lose access to his bitcoins anyway, so in such a scenario, using an online exchange is a better choice but long-term, this will lead to the lose of your coins because exchanges often get hacked.

To sum up, learn how to create a cold wallet, how to keep your seed phrases safely and stick with cold wallet. If you don't know how to do it, then use an online exchange until you'll understand how to create and keep a cold wallet.