Hard to make a bad choice among this lot. It really is a great time to be a Leica M or LTM shooter. I found that the 21mm focal length took some learning to use well. My advice would be to start with the C/V offerings because they are a really low-cost way to see whether this FL is something that you will use. If not, sell and get most of your money back. If so, sell and get most of your money back and upgrade to the Zeiss versions.
Ben Marks
I agree completely with Ben in trying the CV options. Your path would be:
1) find if 21mm or 25mm focal length works for you but a minimal financial outlay.
2) if either of those focal lengths do not work for you, resell here and get most of your money back. Be happy you learned that at minimal cost.
3) if one of those focal lengths do work for you, then see if the optical quality meets your needs (and I bet it will.)
4) if the optical quality is good, be happy that you are satisfied with the lowest cost option being the CV.
5) if you think the optical quality of the CV lenses need improvement (and I think you will not), then pay the money to see if the Zeiss meets your needs. Then sell the one you decide not to use. You can be happy that you made an educated choice in the money you spent.
FWIW, I have 2 Zeiss lenses currently, a 35mm f2.0 and a 28mm f2.8. I have 3 CV lenses currently, a 28mm f3.5, 25mm f3.5 and a 21mm f4.0. Optically I can see almost no difference in my everyday shooting. I use the 25mm and 21mm very little so am happy that I did not buy the Zeiss equivalents to sit on the shelf.
Lastly, remember there are real tradeoffs between lens speed, weight & size, and cost. I do not see optical quality as one of the tradeoffs as they area all better lenses than we are photographers. Make an honest assessment which tradeoffs are really important to you. Do not automatically assume that a faster lens is better. You may use that extra speed so little that it is not worth the weight which is there all time. And cost is an ever present factor. OTOH, if you are one of those who believes the limiting factor in the overall quality of your photographs is that you only spent $350 for the lens when you could have spent $1,000; then buy the more expensive glass. Then you will have to find a new excuse.