Must be an e430 Sport, the base really wont do 6.1 seconds unless its brand spanken new. A stock Mark is roughly a second slower. But 0-60 is not a measure of passing ability. At 60mph, HP is where its at. At 275hp its just a touch under the Mark. Sine neither car is new and weigh about the same, may as well just call it a tie - maintenance will have the biggest impact between the two.
The Benz is probably more comfortable, the Mark will feel more sporty. Overall the Benz build quality will be far superior and the Benz will have more "features".
At this point both cars are old dogs and both have a laundry list of known issues with few, if any, unknown common issues. Milage means little at this age.
For the Benz, they love to body rust on the E class. The harmonic balancers can be a big issues if they missed the recall. The front suspension needs close inspection, I think there is a rusting issue that causes some part to fail and collapse the strut. There are many more common issues that add up but I am sure most you learned before you bought and this is a Mark VIII forum
So for the Mark common issues are fogged headlights with decomposed reflective material. Best to replace/rebuild. Air ride is straight forward and easy to fit but on it own can have a list of failure points. One or two common vacuum leak issues (most common is a cheap T-fitting near firewall from intake, another can be the intake tube to throttle body). Depending on 95 built date, valve springs can break. Updated "beehive" style came into production at some point in 95. Transmission is pretty solid but solenoid springs can snap, harsh shifts mean they need to be replaced asap. There are more I am sure and others will add.
As for which is "better", it depends. The Benz is probably a superior car on overall sense when both were new. But at this point its a level playing field. If performance is your desire then the Mark will win with its massive community of 4.6l modifications. When it comes to maintenance costs, they are about the same. I found that most Benz parts are cheaper than the equivalent Ford part. Some are not though. Its when you pay for labor that the Benz can add up more.
Both cars have a community with online directions, tutorials and guides for fixing the most common issues.
