I don't recommend using W7 Backup or it's imaging for either your main computers or portable drives/other devices.
Easeus Todo Backup is excellent. Will allow Partition Images or files&folders Backups. Incremental/Differential backups and scheduling.
Backup to or from your computers to external drives. Doesn't matter for most software (except built-in W7!)
Many people also recommend Allway Sync. It's like Synctoy, except it is supposedly much better (may have a scheduler)