I drove a lot of Mercedes E, CLS, SL, C, ... Most of the time very good seats.
We have now at home a 2011 E-class and a 2010 C-class. The new E-type is a facelift of this 2011 model. They are now going for more sportive looks. In the previous (pre-facelift) E you had nicer suspension and seats in a so called Elegance. In the Avantgarde they were firmer. My C has these type of seat upholstery.
This latest E-type is more the previous Avantgarde-setup. So they went for fimer seats, I guess. You could ask now for comfortseats. These seats have more adjustments. Best are the ones with dynamic contour setup.
I am sure that will make a big difference. Sometimes the showmodels are they ones low profile tires and sportseats. They look nicer in the showroom, but are less comfortable often. So: I would ask for comfortseats and Airmatic and maximum 17 or 18 inch rims (no 19 ")
best regards, Rudy