I have a 2011 M3 (owned a number of them over the years) and I just picked up a 2011 C4S. Before that I had 997.1 Targa 4S.
Our M3 is nice but I will probably never buy another high performance BMW again the M cars go on a serious diet to lose 400+ lbs. The M3 doesn't feel connected to the road like the Porsche. Yes there are plenty faster cars then the C4S buts it's never about that. For example, instead of C4S, I could've bought a GT-R which would smoke 95% on the road straight from the factory

BMW M series make great GT cars..fast, comfortable but I would not call them true sports car and they look like every other BMW. We also have an Audi R8 which we like.

Amongst the sports cars I've owned, Porsches hands down are the best all around cars, period. Fast, handles very well around corners, reliable (knock on wood), timeless design, and every day drivability.