I work mostly with Windows, so that is where I have my core skills. That however doesn't detract me from the "Use whatever tool that works best" philosophy. And I consider OS part of my tool-kit.

In some cases Linux is clearly superior. In other cases I find Windows a much better choice.

It all boils down to two things: What you know well, and what actually gets things done. I see no reason to artificially limit my choices and make my work harder.