What is your favourite UI/UI design?

[Axiom]

A quite simple topic that popped into my head as I was just thinking about Google's new Material Design. I see lots of apps supporting it now, and though I thought "eh" at first, I must say that it's grown on me.

However, while the new OS X designs grew on me, looking back at Snow Leopard, I must say they now look "eh". Discuss here, your favourite UI (user interfaces) or designs of UI. Even if you don't like to use a UI, you can still appreciate its design as I did with OS X.

My personal favourite right now is material design. When apps support it, my god it is so natural and beautiful. Especially on my LG G2 (now running CM12 aka basically stock Android). Absolutely gorgeous and scales nicely based on screen size as I've done with my website and their new polymer toolkit.

So yeah, what's yours?

[Doodoxing]

I just love Aero Glass stuff, because it makes the desktop more pleasant to use. Pity, that they dropeed it in Windows 8...

From mobile UI i mostly like Material Design from Google.

[Julia Pseudo]

I really like the old Mac OS X look, probably mostly because I grew up with it. It did have a more sophisticated look than most operating system UIs at the time, though.