As a previous long-time BMW owner (E36 M3, E46 sedan, E90 sedan), I have recently gone down the Audi path after moving to Colorado. I thought I would pass along my impressions of my 2007 335i vs. the 2012 S4 I just bought. Both are wonderful cars and you can't go wrong with either one, but they do have their distinct strengths.
First, the cars (I won't go into gory detail...both are loaded and comparably equipped):
Audi: 2012 S4 6-speed
-White with red/black interior and CF trim
-Prestige package and Sports Differential
BMW: 2007 335i 6-speed
-Grey with Terra interior and aluminum trim
-Sport package, cold weather package, etc.
335 strengths:
1. Steering: the RWD BMW simply has better, more alive feeling steering. The S4 steering is good, just a bit heavier and less precise IMO. This is likely an artifact of AWD, as I drove a 335 x-drive and noticed heavier, less precise steering as well.
2. Shifter: Frankly neither shifter is as good as, say, an S2000 but I thought the BMW shifter was a little bit better.
3. MPG: The S4 is a little thirstier, especially when you drive it like it's mean to be driven. My 335 would routinely get 28-29mpg on the highway. The S4 gets more like 25-26 mpg.
4. Engine sound: Frankly, both are too quiet from the factory but the 335 has a growl that the S4 does not. The S4 is really too quiet.
S4 strengths:
1. Interior: I know the buff books like to rag on the B8 interior as being dated, but I think that's just because they are used to it. To me, the S4 interior is simply better than the E90s. And the Red/Black...stunning.
2. Engine: Both are great engines, but I find the super-charged 3.0 in the Audi to be a bit more impressive. Very linear power delivery all the way to 7K, no lag, and very smooth.
3. Handling: My car has the sports differential and it is spectacular. It eliminates all the under-steer you associate with AWD Audis and simply rockets the car around corners. It almost feels like the faster you go, the tighter you can corner.
4. Back seat: This might not matter depending on how you use your car, but the Audi has a much better back seat for people to actually sit in.
5. "Tune-ability": Although the S4 reflashes are not cheap, it's a piece of cake to get 400+HP out of the Audi.
There you have it, my quick-and-dirty after owning both cars. Again, both are great cars and you can't go wrong with either one. But so far, I'm very impressed by the S4.
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