None!
@schmorp @Gargron Me too, it improved on 7 but walked back some of the mistakes from 8.
10 is just trying too hard to be its own new thing, constantly changing settings/control panel functionality and still wildly inconsistent UI. I work with mostly Windows 10 computers at work, but my own work computer will be staying with 8.1 as long as I can get away with it.
@bluestarultor @malin @Gargron DOS was clearly the best part of 3.x

@polychrome It was where all the games were!
Although I discovered some of them could actually be run from either side. IIRC Castle of the Winds 2 was one of them. But mostly I only remember Windows having Solitaire and MS Paintbrush.
@Gargron Mine was a 286 which I got given in parts and a set of discs with DOS and Windows 3.1.
It took me a further six months before I got a mouse, so I've always been good at finding the shortcut keys!