I’ve been using standard Gnome Disk and KDE Partition manager but both uses not sparse images. So if you are doing backup of 40Gb disk with only 9Gb used you will still get image of size 40Gb that is little bit wasting of disk resources from my point of view.
That is reason why I recently did some investigation and started to use partclone tool for this purposes. It doesn’t blows final image size if source disk not uses full capacity.