Quick Question, is this a W124 or w210? If so, I would deffinitely suggest the Firestone Firehawk SH30. Gives tons of mileage (50,000 mile warranty) Great in Wet and Dry, and H-rated All-Season. Is very good compared to many of its counterparts. These tires are a little more biased to Touring then High Performance, but It better suits the characteristics of your E300 Diesel. Also, they are nicely priced.
FireStone Firehawk SH30 Rating and prices at TireRack
According to what model this is going on, I would recommend the following sizes:
w124:
205/60/15
w210:
215/55/16
(235/50/16, if you wanted wider w/o changing wheels and adversely affectomg your speedo, however, snow traction would be altered due to the wider footprint)
The Firestone are available in the 205/60/15 size, but not the 215/55/16s.
For 215/55/16, I would recommend one of the Birdgestone RE950 highly, unless you don't like direction tread patterns because of the rotation limits, then I would go with Dunlop's new SP Sport A2.
Dunlop SP Sport A2
Bridgestone Potenza RE950
Hope that helps, Good luck.
Safe Driving.