An operating system is a link between computing hardware and the applications that run on it. So it's essential To determine which operating system is best for your dedicated server, for that consider the following:

Purpose of the server:
The server's primary function will determine the operating system's choice. For example, a Linux-based operating system like CentOS or Ubuntu may be a better choice if the server is used for web hosting. On the other hand, if the server will be used for hosting applications that require specific Windows-based software, then a Windows-based operating system like Windows Server would be more appropriate.

Application requirements:
If your application is built for a specific operating system, you should choose the corresponding operating system.

Performance:
Consider the performance of the operating system. Some operating systems perform better than others, depending on your server's hardware configuration.

Familiarity and experience
If you have experience working with a specific operating system, you may prefer to stick with it.

Linux is also much cheaper to run than Windows since it is open-source. Ultimately, the best operating system for a dedicated server will depend on the specific needs and requirements of the server's intended use.