a) It just keeps on working.
b) They are conservative with new technology. This means that by the time things hit debian theyre well thought through.
c) The community behind debian is principled.
d) The debian package repository is very exhaustive.
e) They offer a small net install iso which is ~180 megabytes. This makes a fantastic foundation for a minimalistic linux install with a tiling manager (without pulling in monstrosities like libre office).
In the past we started with Redhat then Centos, that was back in the day of more simple RPM where you had to resolve dependencies manually. We were mainly using the unit as an internal LAMP and file server, nothing exotic.
After Ubuntu went into creating server versions we went that route. The on-line community was way more active and the package manager just worked.
Ubuntu is definitely a route of lower frustration when things go wrong.
Personal systems: Gentoo. (easiest to customize and automate for me, time investment required.)
Nginx/Apache: Debian. (stable security updates, minimal install)
MariaDB/Postgres: Debian. (security updates, stable branch, well tested.)
Other unless I am stuck with RPM: Debian (long term stability)
RPM: Fedora (works, but EOL is always soon, so make sure the server does only one thing)
Mint 15 on my laptop
Switched my home desktop to Debian. Would want to switch my work laptop to Debian for longer term stability but not sure if all drivers are available (couldn't get Realtek HD SPDIF to work on my desktop). Can anyone with a Thinkpad T500 confirm that it works flawlessly?
I don't particularly have any issues with stability with it, despite its reputation for being bleeding edge.
On our servers, we use CentOS though, so consequently, I keep a bunch of CentOS virtual machines for testing too. I think CentOS was chosen for our live servers because of it's stability.
I also have a centos 5.x box running personally
though if you are not a "beginner", i highly recommend ArchOS https://www.archlinux.org - by far the active-est community out there