I will base my choice on looks, because that's the point of these cars. The price difference between the two cars would mean the CLS could also be pitted against the A8, but they didn't because they are both "4 door coupes".
I'd take the CLS, this things looks incredible while the Audi, sadly for them once again, looks pretty much exactly like every other Audi 4 door car, except it's longer and has a sloped roof line.
It's a shame for Audi that it's almost impossible to tell their cars from one another.