The 'best' backup utility is the one that does what you want it to do, the way you want it done.
Tar will make multi-disk backups (but you may need to write a script to tell it what to do when it reaches the end of a disk). Tar backups, especially if compressed, are one large file. If one file is corrupted, you may not be able to access the rest of the backup.
There are other open-source options as well as commercial.
I prefer DAR because I can get backups done the way I want. Dar is a set of bash scripts; easy to set up if you read the README carefully (it also serves as a tutorial).
Back up the directories most likely to change frequently, or which contain configuration information. /home, of course, but also /etc (unless you really want to go through all the configs of your apps again if you have to re-install). Perhaps also /var (leave out some of the logs unless you need to save them), and any apps you installed from some source other than install disks.