Windows 10.

Tried Linux for a while (Mint, Ubuntu). Mainly because I had a really low power laptop and was too poor to afford one fast enough to run Windows well. This was back in 2007/9. I finally sorted my life out, got a better job and bought a decent desktop. Windows ever since.

I have just built a sick new rig (Ryzen 3700x, etc.) and run Windows 10 on that.