Debian is a widespread Linux release, that is used mainly on PC's, but many people have started using it lately as a web server OS as well, due to the stability and security it offers. The latter is a consequence of the fact that Debian is developed and supported by countless qualified volunteers worldwide, so that any patch which is necessary to fix some issue is released within a couple of days. The same community will also help with any question or issue that a user may ever have, since they can be contacted via email using mailing lists and a competent response will be sent in around 15-20 min. The advantage here is that your queries will be responded to by the same people who have made the Operating System itself and they have an in-depth knowledge of how it works. As Debian is absolutely free, you won't need to pay any license fees to use it and you can personalize 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 readily available for it.