Question: I am a bit confused. I am using iCloud Drive to store backups from my internal data each time the user clicks 'backup'. This doesn't work as I would like to, because sometimes it just doesn't sync between the devices and users that click restore get's their old backup.

Now I've read about iCloud Documents and that you could trigger a sync manually from there. What's the difference between iCloud Drive and iCloud Documents for me as a developer? I just don't get it..

I am not sure whether it would be better to store backups with iCloud Documents...?

Answer: 
I think iCloud Drive provides the service that user can edit document through specified interface.
In contrast, iCloud Documents Storage provides a kind of service that stores some confidential or unchangeable data for application.
iCloud Drive - Apple's Cloud-Based Service for consumers. Typical known for their ability to sync between different devices through storage in the Cloud.
iCloud Document - A single file of UIDocument type.
iCloud document storage - Service that provides developer access to iCloud for their files which are usually UIDocument type or file packages which are of NSFileWrapper.
iCloud - Cumulative set of Apple's cloud services consisting of iCloud document storage, Key-value storage, CloudKit, Core Data.

* So above question is not relevant as they are not comparable technology.