Although my favorite free Unix-like is NetBSD, I have a great deal of admiration for what Debian does and how it does it. To me, it is one of the best Linux distibutions, along with Slackware and Arch.
Debian and Slackware: both roughly same age (Slackware releasing first). Contrasting package management, patching policies and governance models. I find the stable releases of both to be, well, stable.
