* 1st - AmigaOS 4
* 2nd - Maemo 5 (on Nokia N900)
* 3rd - Windows 7 (not Win 8 or Win XP)
* Forth place - Windows 2000 (WinXP classic look) and AmigaOS 2.1 with MagicWB
:hat:
Ah Maemo 5, the little golden child that was left as an orphan...
Still love my N900, even though I finally bit the bullet and went Android.
I'd have to throw my vote in with Enlightenment as well for the most 'beautiful' GUI. Though yes, the functionality, while solid for what it does have, is missing some key components that are part of what most consider a full desktop solution... then again, so does Windows.

As far as simplicity and functionality, my vote would be Gnome-Shell. It really does just stay out of the way and let you do what you want to. The latest versions haven't even had me want to change the default theme, where as the default theme in OSX drives me nuts.
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