They're both good cars, the W124 is bigger and has more of that solid Mercedes feel, the W202 is more modern and feels nimbler. Between the two, it's my experience that the C280 will probably require less work to keep up than the 300E, if for no other reason than age. You'll probably also have an easier time finding a low miles C280 than a low miles W124. If it were my choice, I'd probably try to find a good 2000 C280 sport.

Anthony