I'm an interior freak and see the interior of cars the same way I look at interior of houses. Qualitywise the A6 stands out and even without sitting inside the car and touching the interior one can see sense it's top notch quality.
The 5er has a very modern looking interior but it is simply too sterile for my taste, and the fact that you can't get the whole dash in beige(or the same colour as the rest of the interior) bugs me.
Finally we have the E-class interior which might not be as superb put together as the A6 interioe but there's something I like about it. With its curvs and smooths lines the interior feels so down to earth. It makes me feel so calm and comfortable.