Debian is a well-known Linux distribution, that's used mainly on desktop computers, however numerous people have started using it lately as a web server OS as well, due to the stability and protection it supplies. The latter is a result of the fact that Debian is developed and supported by thousands of qualified volunteers around the globe, so that any patch that's required to fix some issue is released within a few days. The same community will also help you with any question or issue that a user may ever encounter, as they can be contacted through email using e-mail lists and a qualified response will be sent in around 15-20 minutes. The advantage here is that all your queries will be addressed 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 free, you won't need to pay any kind of license fees to use it and you will be able to personalize 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 readily available for it.