Testing is pretty stable for something named "testing" and unstable is remarkably stable for something called stable. Well, except that one month every 2 years after release where all that was frozen for release gets unfrozen..

And it being stable is not only important feature. The upgrades just work, better than in any other distro I tested (unless you make frankendebian but even then surprisingly often it also "just works". Slap unattended-upgrades package with some settings and you can basically forget it if it is just some service