If you're buying a car at a dealer, also take into account the level of service you are given at this dealer. In my opinion this is very, very important. I bought my Mitsubishi Lancer a bit on impulse... and I didn't really pay much attention to the dealer, I was inexperienced. Not to say I made a mistake, I love the car - it's better value than every car I've compared it to. But - the dealer is absolute sh!t and for that reason I will never buy a vehicle from them again. There is a Mitsubishi dealer I know of that is good, and I may buy an EVO from them... but otherwise I won't even consider a Mitsubishi, based solely on the experience of being shafted at numerous Mitsubishi dealers.
Now, for bang-for-buck the Mitsubishi Ralliart is hard to beat, in terms of performance as well. However if you are looking at A4 and 325, I would definitely have to recommend the 325. I say this not having test driven the Audi, though. I did test drive the BMW 325i and I absolutely loved it. Had I the down payment at the time Id probably have traded in my Lancer and got the BMW.
The handling was amazing, even at 170KMH. And that's another thing.. I showed up to the dealer in my baggy sweater and baggy jeans, greasy hair and he still treated me professionally and with respect, and offered a test drive. The service at that dealer was exceptional. The salesman was not pushy nor shady. I would buy from them just for that level of service. Also their warranty service was amazing where I went. Basically you will only ever pay for your brakes or tires or whatever. Everything is guaranteed (they are confident about their product) - they offered free lifetime oil changes, even though it only NEEDS an oil change every 20,000KM!
I don't know how Audi is but unless the driving feel and customer service is at least better than BMW, I would get the BMW. The BMW also had exceptional value. For a base price of $35k CANADIAN, the 320i was incredible value. However I test drove the 325i with sports package (17" mags) fully loaded for $45k CAN.
I don't know about the AWD systems of Audi and BMW - I would take just the RWD BMW. They still have a whole buttload of traction and directional stability control technologies you may want to take into account. A backwheeldrive BMW with good tires will fare very well in poor conditions despite not being AWD.
I guess anything is better in the winter than my lancer with 14" donut wheels and horrible (and bald) tires...