If you have a kit already (!) only consisting of modern Zeiss lenses, the choice is obvious: Go for the 21mm C-Biogon !
Cheaper (?), allows TTL metering, higher corner sharpness, and less (or no ?) vignetting.
In case, the 35mm Summilux pre-ASPH, 40mm Summicron-C, 50mm Noctilux, 75mm Summilux-M are lenses you like, the SA would be my recommendation.