I will start by saying that there is no such thing as the best (or the worst
) O/S for using as a server. It all depends on your needs.
Choosing what system will host your website is about answering a lot of questions to get a clear picture of your requirements.
What is the amount of liberty do you have for trial and error? Do you have an existing website or you are about to build a new one? Is it about a simple personal blog or a commercial site (in this case check also for your internet service fair usage policy and if your internet contract has clauses prohibiting commercial use, restricting to personal use only)? What do you want to to do with the Web server and what tools will you use? Technologies like ASP, .NET, MS Access, MS SQL Server, etc. point towards a Windows server solution, while PHP, Perl, MySQL, etc. have Linux as their natural habitat (even if you can find all that in a Windows environment too)? Are you going to maintain your O/S on your own? What is your level of expertise on administering a Linux or Windows server? Are you willing to pay for your O/S or you will go for a free solution? Is security that much important that you would consider going for a security-oriented operating system?
A stable Linux distro with long release cycle and long term support will remove much of the O/S administration clutter, leaving you with the necessary "piece"
of mind to focus on your website development, maintenance and administration.