Well this one for me is a no brainer.. First of all i also wouldn't want to be lumped into the BMW stereotype as well and the fact M3's are getting more and more common. Then comes the RS4 with a rear biased Quattro system oh so sweeeet.
Not to mention that 40valve V8 puttin out 420bhp and redlining at ~85000 rpm.. Oooh Yea! hopefully they will be rare like RS6's

 

Both are (will be) heavy pigs, but given a choice (with the incomplete details that are known today) I'd take the Audi.