Having owned both, the C63 is more expensive to operate. I'm getting notably worse gas mileage and tire wear is more pronounced. The C63 is covered for wear and tear (brakes included) in Canada whereas the M3 was not. This may be different in the US. However, regular maintenance was covered on the M3 (oil changes) and not on the C63.
If day to day costs are how you determine the better DD car, the C63 loses IMO. If you define the better DD car to be the one that sounds aggressive and has more easily attainable power then, IMO, the C63 wins. What makes a car a better daily car is subjective and what one of us values will be different than another. Heck, what I value in a DD car changes from week to week
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