I was driving the A4B7 before this E90 318.
Was not even planning to change my ride until the test drive. The E90's handling really impressed me and the rest is history... the hum coming from the BMW's N46 is really very different from the A4B7's, if I may put it, sounds and feels like any in line 4.
The A4 is a decent car. But somehow, I like the E90's driveability, like they say, a driver's car. Very accurate steering. Construct-wise, I feel that the BMW is more solidly built.
Interior aesthetics, the Audi wins but to me, it is really good to have. I think the E90's serves its purpose very well. Exteriorly, the Audi is getting prettier and prettier but then... probably too pretty.
Mods wise, the BMW has more to play with altho the Audi market is picking up.
Lastly, I have not tried PML's service but reviews do not seem to good. Premium's service is very good actually.
So, for the buyer, really depends on what you are looking for. Looks or drive.
Cheers.