I think the "Aero" UI in Windows Vista was the high point for Windows UI. The OS ran poorly and its fundamentals (like all Windows versions) was junk, but the UI looked really nice. This modern flat stuff is crap.
Aero was still used in Windows 7, with some additional nice features. But I agree, it was the high point of Windows for me - jump lists, Aero Peek, window snapping. It was all transformative.
Then they threw the baby out with the bath water in Windows 8.
I never really used Vista, only 7, but it seemed like 7's UI look was watered down compared to Vista: Vista looked prettier to me from what I saw of it.
I started in the mid-90s, and though I didn’t use 95 much I did use 98SE (which is aesthetically very similar to 95) and 2000 plenty.
For releases with the classic Windows look, I think 2000 is best. It makes a few refinements to the theme that at least to me make it more pleasant to use than 95/98.
I started well before Win95. I can still see that Aero was MS's peak UI, even though I never seriously used the OS myself (my workplaces all seemed to skip Vista).
Then they threw the baby out with the bath water in Windows 8.