I liked the physical model they used in the 60's, it's colouring and texturing gave it a real depth and toughness - it felt old, but horribly destructive. I also liked the simplistic and robotic way it moved, like it treated space as a three dimensional grid.
And it's remarkable how well the original planet-killer model worked, because when you take a good close look at it, you realize it's basically a roughly carved wooden cone wrapped in clear adhesive tape or plastic sheeting. It's an amazingly crude construction that turned out to be amazingly effective. I can't see it working too well in HD, though.