Many. There's a reason why sysadmins love GNU/Linux. I don't think I would recommend "backing up Ubuntu", however. I would much rather have a different backup plan for homes and system, since homes are usually much more important than the system. If the system gets lost, you won't usually have lost anything, since it's all free software. If you do have system databases like MySQL configured, that's something to consider. If you haven't made system-wide configs, then it's not so important. The worst thing that can happen is that you need to redownload and install. All user data, including settings, are stored in their homes.
Backup homes frequently. The system doesn't usually need that frequent backups.
The first time you create a backup, there will be very little difference between different tools. All data needs to be copied the first time. That means many GiBs to be copied. The next time, however, it starts to change. If you use an incremental backup solution, you will only copy data that's changed since the last time. I'm deeply ashamed of it, but I haven't tested Deja-Dup well enough to know if it does that.
rdiff-backup is a CLI solution that provides incremental backups using rsync. It's quite efficient.