Well, environment secrets are specific to an environment in Github Actions which allow you to run different configurations for jobs in a single repository, e.g. to deploy to staging first and later to production.

Repository secrets are specific to a single repository (and all environments used in there), while organisation secrets are specific to an entire organisation and all repositories under it.

You can use environment secrets if you have secrets which are specific to an environment.

If you are unsure, you could also start with repository secrets for everything. If you later introduce different environments which require different secrets, you can move the repository secrets to the specific environments. Due to the inheritance chain, this should be transparent to the jobs.