Contax IIa, Carl Zeiss Biogon 21mm f4, 1/250 f16, Ilford FP4 125
How do people think they compare with the more modern skopar 21mm that were on offer a few years ago ?
Thanks for that.They are both excellent lenses in my experience. Having click stops on an easily seen f/stop ring on the Voigtlander lens is certainly more convenient than the placement of the f/stop settings and lack of click stops on the Zeiss Biogon, but optically I think I like the Biogon just a little bit better. This is subjective and based on the two lenses that I own--others may feel differently.
How do people think they compare with the more modern skopar 21mm that were on offer a few years ago ?

I think they are very different lenses. There are 2 Color Skopar 21s, and both are modern high contrast lenses. The 21mm f4.5 Biogon is not high contrast and appears to be less sharp at larger apertures. If you are considering the Biogon, then you are either shooting a Contax or Nikon RF, so the choice is fairly simple: get the Biogon for classic rendering or get the Color Skopar for modern rendering.