As with many such choices, the decision is subjective. However, I highly recommend VS Code. It starts as a lightweight editor but can become quite powerful as you explore its features further.
For the workshop, you might find Codespaces particularly useful. This feature allows you to edit and run Sage code directly in VS Code, either in the browser or locally, without needing to install anything. It’s free for up to 60 hours, which should be more than sufficient for the duration of the workshop.
Get started with Codespaces here.
If you can persuade one of the Sage admins to spend $2, they can activate prebuilds. With this enabled the Sage environment starts immediately, rather than requiring a few minutes for building (https://github.com/sagemath/sage/issues/36978).