I don't know... the C63 has some amazing numbers and its aggressively priced...
However my friend owns a C55 and that car was in the shop like every other week. He lemon lawed it and got an E55. He hasn't had any problems with it so far but he still wouldn't recommend getting another Benz.
I'd probably get the M3 because it looks hot and is more race car oriented, but thats just my 2 cents.