More then 80% of the desktop computers in the world run some sort of Windows operating system.
You won’t have any problems finding support.
The most prone operating system for spyware and virus applications.
More secure than Windows due to its UNIX base
Almost no spyware or virus applications.
Way more secure than Windows XP and even OSX.
Everything is free
Limited support for proprietary applications
The latest and greatest hardware is typically slower to reach Linux.