Onurleft... the C63 is definitely the 'king' in the TQ area... but is slowest around any roadcourse... much heavier than both... and get's horrible gas mileage.
My M3 would get 19 MPG.. ISF 20-21MPG... Seems as though most C63 are lucky to get 16MPG... for a DD that's tough.
You are right 'better' is completely up to the owner, as so many different wants/needs. None of these would be a 'bad' choice!
Peace,
Dave