Debian is a widespread Linux distribution, that's used mainly on PC's, still lots of people have begun using it lately as a web server OS as well, because of the stability and security it supplies. The latter is a direct result the fact that Debian is developed and supported by countless qualified volunteers worldwide, which means that any patch which is necessary to fix a certain issue is released within a couple of days. The very same community will also help you with any question or issue which a user may ever experience, because they can be contacted via electronic mail using e-mail lists and a qualified response will be sent in no more than 15-20 min. The advantage here is that all of your queries will be addressed by the same people who have designed the Operating System itself and they have a detailed knowledge of how it works. As Debian is provided for free, you won't have to pay any kind of license fees to use it and you can customize it as much as you want or need. This is valid for both the Operating System as well as the 30.000+ software packages which are available for it.