Hi Jo-anne,
The S class is only available as a saloon - and this has self levelling air suspension as standard.
The E and C class can be either a saloon or estate, and self levelling suspension is fitted to the estate models.
I tow our Eriba Triton (1200 kg) with a C270 CDI and see 50+ mpg on a long journey, and on the drive back from the caravan dealer after it's annual service saw 41 mpg towing on dual carriageways and A-roads.
But usually I only!! get 36 mpg when towing - and of course it's an automatic. People with the C220 usually see closer to 30 mpg towing - the bigger, more powerful, higher torque engines are much more suited to towing.
Robert