Debian is a well-known Linux distribution, which is used primarily on PC's, however a lot of people have started using it lately as a web server Operating System too, due to the stability and protection it offers. The latter is a direct result the fact that Debian is developed and supported by numerous qualified volunteers around the globe, which means that any patch which is needed to fix some issue is released in a couple of days. The very same community will also help with any question or problem which a user may ever have, because they can be contacted via email using mailing lists and a qualified response will be sent in around 15-20 min. The advantage here is that your questions will be addressed by the same people who have created the Operating System itself and they have a detailed knowledge of how it functions. As Debian is provided for free, you will not have to pay any kind of license fees to use it and you'll be able to customize it as much as you want or need. This is valid for the Operating System as well as the 30.000+ software packages that are readily available for it.