I find TM1 Rule worksheets (XRUs) as the best place to write my rule files.
They allow for easy formatting and commenting for your rules.
One other advantage is that you can keep backups of your rules by just copying your worksheet. This allows you to change your rules, test them out and if it all turns to custard, revert to the backup.
You can also have multiple worksheets within the workbook for different scenarios e.g. a rule to save for the Forecast and a rule to save for Budget time.
