I actually find the steering my C63 much better weighed and responsive than the one in my M3. I didn't have M-dynamic mode though.
At the limit on the track, the M3's steering was slightly more precise, but that was likely the weight and traction playing in as well.
Current: 2012 C63 AMG PP | 2012 F25 X3
Past: 2008 E92 M3 | 2009 E90 335i | 2007 Z4MC | 2002 GTI 1.8T | 2000 Celica GT-S | 1999 328i | 1990 Corrado G60