I use debian on servers. I do not use debian elsewhere. Debian lacks a lot of the quality of life stuff that ubuntu based distros have. I cannot just add-apt-repository a ppa. The packages in the default repos are very old.
It makes up for this, by not doing the stupid garbage that ubuntu does. I can edit /etc/resolv.conf whenever I want. I can install firefox through apt.
It is also much more stable in my experience, and pretty lightweight.
I especially like that when I install it i get the option of installing no desktop environment as an easy choice.
Generally, good server OS. Would not use elsewhere.