Some people in this post are talking about M being the purer sports car with more finnessse, the better drivers car blah blah blah. ALL that talk is for very experienced track/race drivers and not the average driver, the average driver wouldnt come close to either cars maximum capabilities.
Only at maximum attack does the M3 show better balance through the corners compared to say the C63.( I'll use the M3 vs C63 as i have personnal experience with them.) The average driver would lap any given circuit quicker in an AMG than thay would in an M. Why do i say this?? cause ive now driven both The M3 and the C63 around Donnington Park in the UK. The C63 is easier to pilot as the gearbox is wonderful to use, is considerably quicker in the strights and unless your 110% commited to race is, just as quick in the bends.
A friend and i drove both cars back to back and both of us could drive the C63 quicker ( allbeit i was the quickest

).
I'm not saying a didnt enjoy the M3 because i did... alot. However everytime i stepped into the C63 i became giddy,( the feel the NOISE omg the noise ) and everytime i got out, i just wanted to get back in. I didnt have those fellings for the M. It just doesnt have the same presence about it.
The tyres also make a big differnce to a car, all M cars come with pilot sports, which are a fantastic tyre, some AMG come with yokos which are pretty shit compared to the michelin. So M give the customer a better tyre which should be congratulated and AMG should do the same thing which they dont.
When the C63 has an lsd and sports suspension it was just as fast as the M3 around hockenheim, i just think AMG feel more of there customers will drive on the motorway and not track. M tends to have a younger demographic ( the petulance of youth eh!) and they are constantly trying to relive the E30 and they get further away each model they bring out.
oh and one last thing before i bore myself anymore

anyone who buys an M3 or C63 will be very happy. Both companies have produced products to be very proud of.