craftsmanship! they are built better with better material. the wood and it's finish, the metal instead of plastic, the leather headband, even the engraving of the letters, even the black mesh covering the drivers wont look as dirty as the new white ones. i think more attention was given to them all around and you had a better shot of getting a consistently well built headphone where as the newer models are almost a shot in the dark especially with the look and finish of the wood, again from my experience.
sound is a little tricky cuz im not sure people know whether it is in fact the drivers or whether time and use makes them sound smoother than the newer models.
to me and most the vintage ones sound and look better!