I don't know much about the uppity uppity BMW's because they cost to much and require to much maintenance. To the person who said they preferred a highly tuned small motor. Highly tuned = expensive, overcomplicated, and fragile. I built a 500+ horse 8 second 1/8 mile car for under $5,000 US. The only reason it isn't a 7 second car is because the car is a 4500 lb 72 Torino.
Corvettes are a different breed of car than the BMW. When it comes to a yuppie cruiser the BMW is a good car, but if performance is what your after, and not as an afterthought, then the corvette is a good way to go. It's like a leer jet vs. fighter plane.
The third and last point I have is that when it comes to who is faster, leave the stock cars out of the equation. The M3 is almost peaked in performance, while the Corvette has a LOT more left under the hood. However, there are a lot more cars out there that have even more left on the table (damn emissions regulations that euro cars don't have to follow) like the Mustang, Charger, Camero, Firebird. Even the rice burners can be made into rice rockets cheaper than a kraut can. Even trucks can be made into real street fighters. I can't tell you the number of small block V8 that are in rangers and s10s.
So buy what you want and be happy.