I have had an A4 saloon with 19" rims, it was a hard drive, now that I have a 156 Veloce SW with 17" allys, I have noticed it is not as hard a ride as the Audi. I do enjoy the road holding with the 156, it seems to go round corners as if on rails, whereas the Audi being heavier does role a bit. Depending on how much you are prepared to throw at the Audi Avant go for the S-Line model as it has uprated suspension. As I am only new to Alfa's and seen the cost of the servicing I am suprised as the cost is not as bad as I thought. My last service on the 03 reg 1.9tdi 130 at 75k miles, it needed a cambelt, pads and disks came to £1300.00. That was with my local Audi dealer, the car was under contract at the time.
The 1.9TDI 90Hp is not quite man enough, fuel consumption is good and the torque is better that the Alfa's.
Now being an Alfa owner - I would recommend a 156 over the A4
Let us know how you get on