There is some fairly interesting discussion on the BMW boards (the 335 can be had with RWD or AWD). The consensus seems to be that the
The AWD will
- Launch harder
- Make you feel warm & fuzzy when it snows
The RWD will
- Have better road feel & cornering (less unsprung weight and better balance)
- get slightly better mileage
- beat AWD from a rolling start (lighter & lower drive line losses)
- Allow you to "drift"
