Pure personal taste. I sold my 1980s Summicron in the 90s because I never used it. I use the C-Sonnar all the time.
Of course, my tastes may have changed too -- but I use the C-Sonnar far more than the DR Summicron I have on loan from a friemd.
Objectively, the Summicron delivers better illumination and better edge-to-edge sharpness. The Sonnar has a 'magic', at least for me, that no 50mm Summicron has ever had.
So no-one can advise you. As already suggested, try the Sonnar first.
Cheers,
Roger