I think a lot of this is subjective and boils down to personal needs and desires. Ive been very lucky to own some fantastic cars over the years (although thats a stupidly ridiculous comment when you consider Andrews "previous"!!!) and ive loved and hated every single one of them and all for very different reasons. Ive always loved owning an M badged car and as much as i enjoyed both E92 M3's and would have more, they were never as "special" as my E46 M3 CSL's - each time i sat in the CSL it became an "occasion" regardless of whether i was heading to a track day or Waitrose. I havent owned a C63 AMG (yet) but ive been in numerous and ive driven a friends on track twice - it equally felt "special" and the noise was very reminiscent of the CSL's induction roar. However, on track my aggressive driving style just didnt suit and we had to change the rear tyres before the 3rd session!! That said it was immense fun, easy to showboat in and always made people look and stare. On the other hand my E92 M3's on track allowed me to gain more experience and further my ability and race craft without constantly thinking i was going to blow it up, head backwards into the barriers or have to replace rubber every hour. All that said, if petrol was cheap as chips, i'd probably still grab the Merc keys every time if anything just to make an "occasion" out of an ordinarily dull daily drive. Sorry, not scientific in any way but my own personal subjective opinion.
By the way, did i mention i drive a "dull as dishwater" Land Rover these days?? Oh how i miss those "silly" days!!!