I prefer
FreeFileSync in mirror mode. It's similar to SyncToy.
I do not recommend continuous backups for onsite backups. To have continuous backups, your backup drive has to be continuously connected to the computer. Drive failure isn't the only thing that can cause data loss. Viruses (and other malware), human error (such as accidental deletion), disasters (fire, flood, etc.), theft, hardware failure, power surges, etc. can all cause data loss. In the case of malware and user error, having your drive continuously connected would mean the loss would also affect your backup drive. The only way to reasonably protect from that is to connect the backup drive only when updating the backup.
Also, it's a good idea to have duplicate backups stored offsite. That will help protect from disaster and theft. To ensure the offsite backups are as up to date as possible, they should be swapped out with the onsite backups as often as possible.
A good compromise for an offsite backup that will also provide a pretty much continuous backup is to use a good, paid, cloud backup service (not cloud storage, especially the freebies). I personally prefer Carbonite.com. It will frequently automatically backup your data to its servers throughout the day. It also has 30 day versioning, meaning any file deleted or changed on your computer will be held for 30 days before being deleted.
Because of the sheer amount of data I have, having to recover all my data from Carbonite would take weeks or months so I maintain an account to supplement the physical offsite backups I keep in my safe deposit box at my credit union. That way, I can recover most of my data fairly quickly from the offsite backups and get any data that was changed or added after I put the backups in my safe deposit box from Carbonite, dramatically redusing the amount of time to achieve full recovery.
