Both are easy to configure and no code is involved.

Formula Fields 


1. Changes in Parent record will be automatically reflected in child records.
2. Change in Formula field cannot invoke trigger or workflows.
3. Formula field values cannot be modified manually.

Workflow Field Updates


1. Changes in Parent record cannot be updated in child records.
2. If the record was updated with workflow field updates, fires before and after triggers one more time. Custom validation rules, duplicate rules, and escalation rules are not run again.
3. It considers criteria before updating the field value.

Workflow field update is recommended over formula field for better performance.