In both cases you have a complete wallet backup which you can use to restore your wallet, unless you are also using an optional passphrase with your wallet.
Both options have advantages and disadvantages.
MicroSD card:
- Advantage: Easy & quick backup and recovery on BitBox02
- Disadvantage: If you want to import the wallet in a third-party wallet you need to use the backup recovery tool
24 recovery words:
- Advantage: Common standard which is accepted by all major wallet which makes it easy to import the wallet.
- Disadvantage: Manually writing down and checking the recovery words can be uncomfortable, slow and error-prone.
In the end it's a personal decision which option you prefer or you just use both options.