Windows

I don't think anyone jumped back to 7 from 10, except for the people whose install upgrade failed and was impossible to complete. Vista, and 8 were both worse than their predecessor, which is why people went back. 8.1 was good though, and that's when people finally started upgrading from 7. But Microsoft is getting far more aggressive. Now they won't let you revert the upgrade after 10 days. If you realize on day 11 that 11 sucks, too bad. You're stuck, unless you do a full reinstall, which most people don't know how to do.