Backup files on Ex2 Ultra NAS - WD Backup or WD Smartware

What’s the best software for backing up files from several PCs to the Ex2 Ultra NAS? WD Backup or WD Smartware or maybe the generic Windows backup tool?

Any drawbacks to WD Backup or WD Smartware?

What’s a link to online manual for WD Backup or WD Smartware?

Thanks

For SmartWare.

For WD Backup, found by using the Knowledge base.