Def 7, it was the first OS used at work that turned invisible.. It didn't need constant defragging, optimizing or registry hacks like 98, 2000 or XP used to. It was a workhorse.
That said, I haven't used 11 yet. My company just announced that this year all PCs will stay on 10 for the foreseeable future.
What did people do before smartphones to pass the time when you were bored?
Would you rather be stuck in the woods with an updated Windows 11 or a Windows 7?