For rust protection alone, I would choose the 124 or 126 over the other choices presented. Get FOUR good aggressive snow tires, no wider than the factory original size, and put a bag of sand in the trunk over the rear axle. A 300SEL would be an excellent choice, with the long wheelbase enhancing front/rear weight distribution and a relatively low-torque engine to keep the driver out of accelerator-induced trouble.

Second prize goes to a 124 WAGON, with the extra rear-end weight a wagon brings to the equation (compared to the sedan).