My girlfriend is deciding which one to get..
both car priced about same..low 50k..

For $55K, a fully loaded A6 is one of the best values out there. The E500 would make the decision difficult, but the Mercedes 3.2 eginine is completely uninspiring.

Even the 2.7T comes out ahead. The new E320 may look nice (although I don't think it's such a departure from the current one) but it's a cow!

Its a rear wheel drive pure sport sedan which I bet will be more exciting to drive than the always planted, never any drama A6.

We have 9 Mercedes in the family... the 320 engine is not enough engine to haul the E class around. You'll have a lot of trouble causing any excitement in the rear wheels with that engine.

that is, it will look like a big scoop of plain vanilla ice cream with no chocolate sauce or whipped cream. Plus the 3.2 engine doesn't even come close to the 4.2.

Reviews of the new E in the european magazines indicate that the new E is a better performer, though still not up to 5 series territory. The Benz 3.2L engine will not move the car like the 4.2L audi motor. ( Never drove a 4.2L benz so can't speak for it).

The Audi is still the more engaging driver of the two.

But then again what is she looking for in a car?

I always get the newer model, in this case the E320, because the A6 will be replaced soon and you would look like a fool driving next to the newer version.
Mercedes are great car, less exciting and personal than Audis but their ride composure is second to none. The most ideal would be E500 if you can afford it. 4.2 is a great car but too bad replacement is coming. It still offer the most classic interior compared to new Merc/Chrysler designs.
One thing about the E320 is that it will give you great gas mileage, my brother easily average 24mpg while most 4.2 owners I know or read about in the forum had hard time getting 18mpg. However, If u love V8 sound and smoothness and classic interior stick with 4.2 for everything else get the E320 and enjoy them for years to come