[swartzentruber]

M3s should be marginally better in bad weather due to having the limited slip diff, although that's likely offset a bit by the higher hp (it's not the DSC, all modern BMWs have that). I've also heard DCT is better in bad weather, due to it's ability to shift smoother than a person. In dry weather, the M3 is leaps and bounds better than the 335xi (I just traded a 335xi in for my M3). Even with my 335xi, I ran snows here in Chicago.

In Pittsburgh, I think you'll be okay in an M3 with snows, although I think some posters are discounting how much worse hills make for snow driving, an area AWD is markedly better. Basically, any RWD with snows should be better than any AWD with AS tires for normal flat landscape braking and accelerating, but I've seen people with experience say AWD + A/S > RWD + snows on hills. Since you'll be driving on snowy hills, if you do get the M3, I think you should really maximize your snow traction. This means 18" (no 19") tires, square setup, and go for the max snow type tires, not the performance winters. If your roads are anything like Chicago in the winter, there's NO WAY I'd consider 19" rims for the winter.

I'd also say it depends on if you can stay home if snow is too bad, or if you have committments where you must get in regardless. Pittsburgh, like most cities in the snow belt, is pretty good with plowing, but if you ever anticipate needing to drive through 12" + unplowed snow, I'd definitely go for the 335xi with snows over the M3 w/ snows.