People really need to think about why they bought an M3......
I think I am in a perfect position to answer this question. I sold my 2007 Audi RS4 last August and have been researching my next car ever since. I just recently placed an order for my new M3 after considering MANY choices.
The M3 is in the class of high-end small luxury-perfomance cars. These cars are not only about going fast. They provide a level of refinement, luxury, style, prestige. Each car has its pros and cons. the RS4 had it's incredible sound, motor and AWD grip. The C63 has it's incredible sound and blistering straight line thrust. The M3 has it's gorgeous styling, intoxicating motor and super-sharp responses.
If you want a pure sports car for a similar amount of money, get a Porsche Cayman S.
If you want to win a stoplight drag, there are A LOT of cars that can be relatively cheaply modded and blow the doors off an M3. So lets not talk about "what car is faster". That WRX in the lane next to you may be packing 500lb-ft of torque.
What makes the M3 so special and such a legendary vehicle is the TOTAL PACKAGE as you can get it from the factory and the overall unparalleled pleasure derived from the subjective driving experience.