Debian is an OS that uses the Linux kernel. Though it is usually set up on desktops, it's being used on an increasing number of web servers as well. The reason is that it's very stable, so a server running it won't need to be restarted for months. Debian is also considered to be one of the most secure Operating Systems out there, since security patches are released within days after an issue is found. This is possible since thousands of well-experienced developers are employed by the Debian project on a voluntary basis and not only do they work on the OS itself, but they also provide 24/7 support by using special mailing lists and respond in 20 min to any kind of question. In this light, you will have top-notch support directly from the developers who know their own platform in detail, and not from a third-party support team. Debian is also one of several Linux distributions with the highest number of packages - more than 30,000. Since the Operating System is free to use, you will be able to modify both the core and all the packages in the way you see fit. In addition, you won't have to pay any license fees.