The E is simply a bigger car-C's the smallest sedans, Es are the mid-sizes, and S-class cars are the big ones. The 280 denotes a 2.8 litre six cylinder gas engine, and the 320 sports a 3.2 litre six.
The '95 E320 was the last of the W124 cars-great cars IMHO, and I have 3 different varieties. I cannot offer you any opinion on the C car; I'vew not ever driven one other than an AMG version, which was a C36. Now that was indeed a very nice car, but quite different from the car you're considering.
"If everything seems under control, you're simply not going fast enough" --Mario Andretti
1995 E500 street car
1986 Porsche 944 Turbo S track car