2000, and 2000 itself. They all worked fine. 2000 was the best CONSUMER OS as it was the best NT ever developed, at the time. 2000 only needed one tweak: add task manager, (well, two, unhide the Admin tools.)
XP was a direct extension of 2000, adding incremental improvements such as a collapsible notification area. Under the hood, XP was an improvement, of course, but the UI in 2000 was perfect.
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