ARKit 2 is out in the wild today. So I am going to say the Unreal demo from Wingnut. Or Microsoft's HoloLens Minecraft demo. More polished than young startups. But I think that magic "a-ha" audience moment is the ultimate.
On a related note, trailer for Tetsuya Mizuguchi's Tetris Effect is pure joy:
https://www.youtube.com/watch?v=Mr8fVT_Ds4Q