Win7. I use LMDE+Cinnamon now and I have it looking suspiciously like how I had Win7. Old habits and all that.
Though you didn't ask, Win2K was the probably the best Windows, IMO. Then came the bloat and the ugly UIs. (I've kind of got used to bloat these days. Storage is cheaper than it was, and LMDE isn't exactly the slimmest distro.)
Maybe I would have liked Win10. Similar to how it was with the old Star Trek movies, it seems like every other version of Windows is terrible, and if that remains true, maybe 12 will be better than 11. Probably not going back to find out though.