If you allow me, I'll say that you would probably better prefer the back of the C4 than the back of the SL, because there are only two seats in the Mercedes !

But these are two great cars to drive, only the C4 has race tracks abilities that the other obviously hasn't

In the other hand, I could drive a thousand miles in a row in the SL and its roof opened without pain, thanks to the massaging and heating seats !