I've had both RWD and AWD cars for the last 12 years here in the Northeast.
Except being burried in deep snow overnight and very steep hills, the only deciding factor for both systems is the tires.
They are your only contact to the surface and if you have crappy tires, it does not make any difference even if you have the best AWD system on the planet. It is like Usain Bolt trying to run in stripper heels!!
That's why I ordered my 535i w/o xDrive and will have a set of Bridgestone Blizzak WS70 or Michelin X-Ice Xi3 if I can find a good deal.
By the way, the best "snow plough" that I have owned in NYC was a 2000 Crown Vic Police Interceptor.
2013 BMW F10 535i - 3.0 L 221 kW (300 hp)
2007 BMW E64 630i - 3.0 L 200 kW (272 hp)
2003 BMW E65 745i - 4.4 L V8, 242 kW (325 hp)
1995 BMW E34 540i - 4.0 L V8 210 kW (282 hp)
1989 BMW E30 M3 non-cat version 147 kW (200 hp)