Debian is a popular Linux distribution, that's used primarily on desktop machines, however many people have started using it lately as a web server Operating System too, due to the stability and protection it supplies. The latter is a consequence of the fact that Debian is developed and supported by numerous qualified volunteers worldwide, which means that any patch which is required to fix some issue is released in a matter of days. The same community can also help you with any question or issue that a user may ever have, since they can be contacted through electronic mail using mailing lists and a competent response will be sent in around 15-20 min. The advantage here is that all of your questions will be replied by the same people who have created the Operating System itself and they have an in-depth knowledge of how it works. As Debian is provided for free, you will not have to pay any license fees to use it and you will 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 which are available for it.