The usual distinction is to use Debian stable if you want to stick to a released distribution, testing if you want to have a rolling release distribution with some safety net and unstable if you want bleeding edge. To get newer software on top of the stable version, there is https://backports.debian.org/ as well.
For my private computers I use unstable, so I get all the benefits of the new version and see compatibility problems or broken updates really early.
At the beginning we had a PPA to test the lastest versions as well, but I don’t have an Ubuntu to test it… If someone want’s to help with it, that would be an easy task to get into packing.