If I jsut had the money for the car?
If I just had enough cash to shell out for a car, I would go for the mustang. Lower maintenance costs, lower INSURANCE, and more "bang for the buck." IE: cheaper mods, and is already faster than the M3. Handling is the biggest compromise but can be modified to perform very well.
If I had enough money to buy the car and then lots of money to spend on the car on top of the cost of buying it....then i'd go for the M.
