If something is doable via a scheduled workflow or a mass update, which is better to use then?

I avoid workflows except for approval workflows or for locking the record. That's just my personal preference.

May I know why? Is it because you have more control in scripts?

Personal preference. Maintaining a script is easier for me. Plus I feel they make the record slower compare to putting the similar logic of a workflow in script. (Haven't really tested it in depth).

I would recommend a scheduled Workflow for recurring changes and using a Mass Update for one-off changes. But Workflows are off course limited, making Mass Update more suitable for handling large amounts of data.

Got it. Thabks both.