Windows
Well, another lesson learnt. For the first time in a long time, I had to boot into Windows 10 on my PC. It was a salutary reminder as to why I made the switch to Ubuntu Linux.
Windows is so slow whatever task is asked of it, whereas Ubuntu just does it in a snap. No fuss, no bother, simple and efficient.
Unless you're a gamer, I can see no reason whatever why you would want to stay with Windows.