How long is a piece of string? This question is a matter of personal preference.
Both use the M104 engine, and both have some head gasket and wiring harness issues.
The C280 is smaller, and handles differently. The E320 is larger inside, and is not as nimble.
Drive both, pick the one that best suits you. Most important is to find the best example of the one you like...
1998 C230 "Black Betty"