Unstable aka Sid receives updates always, I think your thinking of Testing which goes into a freeze period before each major release of Debian.
Sid has been quite stable for me, the packages are much newer than Ubuntu (generally on par with Arch or close to it) and the few noteworthy bugs I have seen over the years have been reported and handled within 24 to 48hrs of said package being updated with the problematic code.
for me personally easier to use installer, proprietary driver/codec support out of the box, faster release cycle, debian stable is too old for me and unstable can break at at all times/doesn't receive any major updates before new releases and so on. Also Ubuntu for the longest time used to be the only distro shipping with good font rendering settings, staring at code all day this actually was fairly important to me
so basically Ubuntu 'just works', if I ran Debian I'd just replicate Ubuntu's default settings pretty much anyway so I can just save myself the few hours.