There are many Linux distributions around. However, I always come back to just one: Debian. The reason why so many people use Debian is the same reason I like it so much: software management. With good old apt-get or the new aptitude, software is installed within minutes. Due to the vast amount of software available even the most obscure software can be installed without resorting to manually downloading and compiling.
But the most important aspect of Debian is it's mantra of stability. It is build for servers. For people who don't want to take risks and prefer stability and security above anything else. This is also the main gripe most people have about Debian: it is often not very up-to-date regarding drivers or the latest software versions. If that is a problem, there is still the possibility to run the testing branch of Debian, exchanging the risk on things getting broken or unstable for the availability of newer software.
As a part-time system administrator, one of the most ideal components of Debian is its installer. Especially the "preseeding" bit. Preseeding is for Debian what Kickstart is for Red Hat and Jump start is for Sun Solaris. It allows a full unattended installation of Debian Linux on any hardware without ever touching your keyboard. This isn't new, but it is much more user friendly as opposed to, for example, kick start.
Debian Preseeding is very well documented and can easily be extended to run your own scripts after installation for some post-configuration.
I currently use it to install hosts by booting them with an USB stick and using a network install. Not only are network installs often the fastest solution, assuming that a local Debian mirror is available, the system is also direct up-to-date.
About setting up a local Debian mirror (requires about 50 GB of storage space on a web server)