I'm answering this based on day-to-day work, rather than all-round.
Getting servers out of the way; they're generally a Linux server distro, not much else to say there as it's quite standard setups.
OSX (macOS) was pick in the poll as it's where I spend the majority of my time. As well as web development work I get involved in design and writing, and because of this OSX has always been the best choice. It allows me to easily get a great working development environment while allowing me to do any design work when needed on the same setup. If it wasn't for design I'd likely swing more towards Linux for my working machine -- though that doesn't mean I'd actually end up using it, it's a different set of variables to consider then.
Yes, I could use multiple OS's for my development/design/writing work, spread over Windows and Linux. However, having all my work needs on one OS that gives me great flexibility is the best choice for me.
There's no right or wrong OS to use, only what best fits your workflow and what you're most comfortable with. An OS decision is just a means to an end.
Note for gaming; I also have a Windows machine at home. Keeps work separate.