I guess I might be able to help you out a little. I went from an E90 (2006 330i Sport, premium, cold weather act.) to a B7 (2008 A4 S-line APR stage 1 tune, plus intake and down pipe) and I currently own an E92 (2009 328xi Sport, premium, CW, iDrive ect.) First, I love my E92 hands down more than the other two. The BMW and the Audi while in the same class are two completely different cars. That being said I really liked both of them. The A4 being tuned and having a few parts was faster than my E90 and E92, however, you could tell that even with the sport suspension the handling and steering feel left something to be desired. The car was not as sharp or nimble as the 330.
As far as reliability goes, I never had a problem with the E90 (drove it for about 25k miles) the audi I only had for about 5-7k and sold it to a close friend of was in need of a car and wanted what I had and that why I purchased the E92 semi- recently. He has put another 10-15k on the audi and the only thing he has had to replace are the tires and 2 wheels bearings.
The audis are a great car, the BMW's are a better car IMHO. It really depends on what your looking for.
If you have any other questions feel free to ask