I just brought a 2010 G37X. Loved it.
I tested A4, 328Xi and G37X. The G37X has the best power! It is the fastest in this group. And the back seat is useable.
The 328Xi has better handling. But it is slow at red light.The 328 rear seats is too small.
I like the 335Xi the best! But because the recall for its engine I did not get it.
And EVERYTHING is option! You have to add 4 - 5 k for it.
The A4 internal is better, but slow. THe back seats is in between.