I've driven both, on trackdays too.
IMO the E90 M3 p*ssed all over the C63. At least I loved driving it much more. It was far more balanced, better turn in and put in some astonishing laps in the right hands.

I loved it in short.
The C63 is a beast and no doubt, maybe the better day to day road car or motorway monster . But for a drivers car I would take the M3 every day if they were exactly the same money.