I would say that neither are good for ANY data "storage". Short term backups of replacable data, yes. But never for anything you can't replace.
While the same argument can be made against any optical media, RW is vertainly less safe than R. Use them only as a 3rd or 4th level of backup for critical data. Personally, I only use them as a 5th (believe it or not) level of backup. R is the 4th level.