Never thought I'd see any love for NT 3.51 For me, it's: Workstation OSes Windows 2000 SP4, followed by Windows NT 4.0 SP6a followed by Windows 95 OSR2.5 (but without the Windows Desktop Update crap that got bundled with IE4.0) Server OSes Windows 2000 SP4, followed by Windows 2003, followed by Windows NT4.0, followed by Windows 2008 As much as I like Windows 7 (and 2008 R2 for than matter), I hate the UI. I hate Vista full stop and XP although good, has given me some problems .... I've had far less issues with 2000 than I ever had with XP. I completely forgot to mention 3.1x .... a solid version, but unfortunately with naff all features. However, Windows 3.1x with Calmira shell on it is superb