To deploy custom setting data that references a profile Id, what should you use?

Using environment variables to deploy custom setting data that references a profile ID is the correct approach because environment variables allow for dynamic configuration of settings and values that may change across different environments. When deploying to different Salesforce orgs, profile IDs can differ, and hardcoding them would lead to errors or need for manual adjustments after deployment.

Environment variables enable you to define placeholders that can be replaced with the appropriate values at runtime, providing a flexible and maintainable solution for referencing profile IDs in custom settings. This mechanism is particularly valuable in continuous integration and deployment scenarios, as it streamlines the deployment process and reduces the risk of human error.

The other options, while they could be relevant in other contexts, do not offer the same level of flexibility for this specific situation. Data Loader, for instance, is primarily used for bulk data manipulation and does not automate handling differences in environment-specific configurations. Manual data migration adds complexity and is not efficient, especially when dealing with multiple environments. Apex code deployment can be useful for executing logic but does not inherently simplify the management of environment-specific values like profile IDs.