[ASalazarMX]

Windows 2000 was my personal favorite. Modern (for its time), lightweight, stable, and the UI didn't get in your way. It took the good things learned since the Windows 95 and pruned the not-so-good ones. I think that was peak Windows.

[heelix]

If you had the drivers, Windows XP-64 was fantastic. A (ahem) workstation twist to Server 2003, which was better than XP and updated version of Windows 2000. I really miss the ISO tweaking tools that were common in the 2000/Win7 days.