I had an RS4 for nearly 3 yrs before trading in for my new '12 E92...
M3 handles better, and has more steering feel. Both engines sound great in their own way. M3 screams, RS a more deeper traditional V8 sound.
RS was better on fuel which I find bizzare when it's 4wd, and heavier.
I think the RS may just pip the beemer on class, especially the interior.
Which do I prefer? Well when it's dry, i make an excuse to go out for the hell of it in the M3 as it's just so good and exciting to drive. I never felt that urge with the RS.
I only miss the Audi in this weather as you can use more of the power and get traction.
Audi is more stealth and only turned heads to those who knew what it was. My M3 draws more attention and admiring glances...