If it is an option, I say keep the M3.
I regret selling my E36 M3 sedan. It was an amazing daily driver. Not to say my 996 isn't, but having a few extra doors really helps with hauling gear and extra passengers with ease. *Edit* Having said all that, they are two very different cars but both I would confidently drive daily.
For what it's worth, my 996 is a daily driver. A lot of people ask why but all I can really do is shrug my shoulders, smile, and drive off.
