Welcome to the forums Werkstatt.
I use Taiyo Yuden 8x +R discs for my most important backups. They have been around a long time, have a proven track record and are well supported in the firmware of dvd burners.
But you should have more than one option for important, archival backups, so I would suggest also using hard drives, possibly external ones that are used only for this purpose.
You might also burn to a secondary type of disc, such as Verbatim AZO 16x media.