I like to answer questions in the unix.stackexange.com community the most since I have been using UNIX and Linux for decades. My favorite OS right now is CentOS 6 with OpenVZ virtualization extensions, but I have used Slackware, and do use Debian and Ubuntu as server operating systems at work.

That said, these days I use Windows 7 on the desktop more than I use *NIX.

I have written MaraDNS, a notable open-source DNS server for both CentOS Linux (but written using portable code, making it relatively easy to port to other *NIX variants) and Windows (partial port).