Your custody decision will be one of the most important early decisions you will make.
Generally if you are trading frequently, so you need to keep your coins available, you will want to use third-party custody. Also, if you are not experienced with managing hardware wallets, cryptographic keys, and redundant backups, you should also consider third-party custody. If you have an engineering background and you can manage the complexity of self-custody and your holding period is several years, then self-custody makes sense.