Debian is a widespread Linux distribution, that is used primarily on PC's, still lots of people have started using it lately as a web server Operating System as well, because of the stability and security it supplies. The latter is a consequence of the fact that Debian is developed and supported by thousands of qualified volunteers internationally, so that any patch that is needed to fix a certain issue is released in a couple of days. The very same community can also help you with any question or issue which a user may ever experience, as they can be contacted via email using e-mail lists and a competent response will be sent in around 15-20 min. The advantage here is that all of your queries will be responded to by the same people who have made the Operating System itself and they have a detailed knowledge of how it functions. As Debian is 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 and the 30.000+ software packages which are readily available for it.