I'd be happy with either of the two - the M3 or RS4. The C63 and IS-F look too bloated, don't have a manual and they don't evoke a sense of passion.
However, if I were to have one, I'd take the M3. Just picture one in white with the carbon fiber roof and RS-GTs or LMs. Dripping with sex IMO. On the other hand, I can't really comment about it's drivability since, well, I haven't driven one. But I did drive my friend's blazing yellow RS4 and that was an absolute beast!