What is the best OS for UnrealEngine to operate on?

I just wanted to know the best os to run UE4 on

Depends on what you want to do.

For development of your project: Windows.
For deploying dedicated server as cheaply as possible: Linux, or Windows AND Linux.
For iOS apps and some other specific uses: MacOS, or Windows AND MacOS.

So, with a little more opinion added, I agree with @anonymous_user_f5a50610.

Windows seem to have best support

Thx, I’ll use Windows

Thx, I’ll use Windows