My DH until recently worked in car rental and had these on fleet as well as the M class. He says that they make the M class look like a tractor and the one to go for is th TD6 HSE model which has the best sat nav on the market included.
He was always going on about them and has one on his wish list (our budget is so far off one though he needs to keep dreaming!) He will be very jealous of you if you get one and if you have any questions he is happy to answer as he drove them alot, despite supposed to it being a desk job he was in!