All 3.
- All servers, hostings, clouds - Linux or sometimes FreeBSD.
- MacOS (I have MacBook) - for testing and debugging Safari on Mac and on my iPhone; At free time learning Swift and iOS dev, also there are some tools available only on Mac. I am using MacBook mostly as a normal typical human and computer user when I am teaching, in cafes, on meetups, etc. The only machine I have no any dev tools, IDEs, virtual machines, servers and everything else installed. I am using Windows machines to blow up CPU and GPU, it is also cheaper to buy new Windows PC and not a Mac.
- Windows on my home and office PCs - yes, I am writting apps on Windows and I have a very solid machine which allows me to run a lot of benchmarks, virtual machines, games with expensive graphics, IDE and all browsers with many tabs and all that at the same time without any lags. I am also using Windows since the beginning and know many secrets from Registry to opening cmd as Administrator only by using some hotkeys. Of course I have Git Bash on Windows installed and many tools are in my global PATH, never using native cmd. Also only with Windows you can test IE and Edge. Well and usually you can play most games only on Windows.
To sum up I am very happy with Windows 10 and new Microsoft politics. Satya Nadella is best what happened to Microsoft.
The only one downside with Windows is case sensitivity. If you commited and uploaded to server Folder and not folder and you now have both, you will have some big problems.