Just a few days ago I was writing about why flat charts can be inaccurate for checking sharpness on lenses. There is curvature, there is human error and angle of position errors. Basically it is extremely difficult to place the camera perfectly parallel to the chart. So, I started doing comparisons by setting such charts in an angle, this helps you check the focusing point and make better decisions on sharpness from certain lenses.
So today, I had the privilege on shooting with the vintage Leica Summaron 35mm f/2.8. Beautiful little lens, not heavy and made of shiny materials. I prefer its appearance compared to the Voigtlander Color Skopar 35mm II f/2.5 but when we look at resolving power (sharpness I mean) you can see that this little $400 dollar lens is a gem. Small, sharp, accurate and available now at most camera stores.
Here is the photo, you can judge for yourself. Yes, the Leica Summaron 35mm f/2.8 has the glow that can make certain photos pretty but if sharpness is your thing, go for the Voigtlander Color Skopar 35mm II f/2.5. I doubt you would be disappointed. I am not.
When it comes to flare, the old Summaron can suffer when pointed towards light sources. In the example below you will see that both lenses shot at f/5.6 are almost identical in sharpness but differ in contrast, again because of the coating on the lens. I give it to the Summaron on this test.
Finally here is at f/2.8, I think I like the summaron again. Specially after its Clean Lubricate Adjust (CLA) and as for Vignetting, they seem to have the same. One benefit of the Color Skpar is that you get the extra half stop of light at f/2.5 vs f/2.8 on the Summaron.