I would agree with all so far, stay away from diesel and make sure you on top of maintenance. I can't speak about the newer models I have a C320 W203 doing 330,xxx kms and no problems so far, only major issue I had was with the ABS module, swapped it and working fine. My aunt has a W204 which never gave her any problems and my cousin has a PDA series E250 with again no issues.
Just take care of it, and it won't let you down, if you do a lot of highway driving the comfort makes up for the price of ownership, when I make POS to south in any other car, I feel tired. Having said that if you want an alternative, the Toyota Camry is an excellent car.