I now have the c63 coupe, it's been with me for 1 week. Both are great cars. To much fun from both cars. M3 is more focused. Better to make perfect drifts and connected drifts on small track. Because u have the engine power under ur feet, and u can simply control it easily. The higher ur rpm revs, the faster the car is, or the bigger drift angle gets. As for the c63, it's brutal, drifting on a small track is very hard. The sudden torque gets u spinning right away. On normal driving, the c63 feels faster because of the torque at low rpm. It just kicks u back. Similar to the feeling in my alpina b3 biturbo. C63 feels faster yet in the race i posted a few months ago, I pulled on the c63 more than 4 or 5 cars. The seats in the m3 are more comfortable for longer trips. Both have harman kardon Sound system but in my m3 it is better, maybe because of the two subwoofers under each seat. steering feel in m3 is better. Dct in m3 is better, though the dct in c63 is a huge improvement over the normal 2011 and bellow c63. Stock exhaust on c63 is ten times better than the stock m3 exchaust. Though my exhaust now is 100 times better
In the c63, u don't have to juice the engine to get the power. It's there on low rpm. In the m3, u must be on the right gear and right rpm to get it moving. This is why the m3 is known as "best drivers car", anyone can race a c63 and go fast. Not everyone can properly race an m car. Many m5 owners that I know lose to stock c63. I made some of them meet again, an I was behind the wheel, the m5 shined like it should
C63 looks beautiful in some angles. M3 is beautiful in all angles
Now, if someone can own both, it would be great because the c63 is so much fun and the low end torque keeps the driver happy
But if I had to choose one, it will be the m3.