The C-Sonnar 50 has the best rendering of any 50 that I own (and I have a LOT of them).In black/white it gives a "lush" glow to the image. I have both the M version and the Nikon Rf version and both are by far my most used 50's. Never had a problem with the so called "focus shift" - as with any lens, you work out what is the "sweet spot" as to aperture and work with that.
The Nokton 50f1.5 is, as Roger states, probably sharper and with some more contrast and "edge" to it - but the C-Sonnar just shines.