Funny this thread is up because I am thinking of swapping my current DD (04 Accord Coupe) for another DD soon.
Here are my 2 cents: You want a car that can do everything your M cant and for me that means more so offroad, towing and carry cargo. Im personally going with a used FJ cruiser or a 4runner.
I love my 04 accord, so much that I did everything to it back in 04 (coilovers, wheels, tint, bolt ons, the works...). Ive outgrown the car, I take clients out to lunch from time to time and my peers as well. Unfortunately perception is everything and the car is way over my age.
For that reason im also considering a C350 Merc as a DD with an extended service.
The M will always be my sunny days/weekend car while my DD, no matter what is it, I plan to take to the pits of hell and back.