Does writing code count as artwork? :-)
If so then Debian GNU/Linux all the way!!
But seriously, although I never used it properly for any decent length of time - BeOS impressed me at the time almost as much as AmigaOS did.
I still wonder to this day what BeOS would have been like if it hadn't been smothered by Microsoft (although to be realistic: BeOS's future still may not have been certain even if Microsoft had played fair, business-strategy-wise).
Smooth running? That's BeOS. Good looking? BeOS did a fair job at that too. Technically brilliant, designed from the ground up as a multimedia OS.
I'm naming my small microcontroller OS after it: BeeOS :-) [it's small, like a bee ;-)]
AmigaOS of course will always be my favourite...
- Paul