Getting back to the objective for this car.
As you need the new car mainly for "work" reasons (i.e., professional image and social standing impressions to clients), you have to ask whether a Beemer or a Merc would serve the need better.
IMO, if your clients are mostly conservative, traditional, and older people, perhaps the Merc would be a better choice, as it gives off a touch of more gentile elegance. Remember that you have to drive them to lunch, so would they feel more comfortable in a classly Merc or a sporty Beemers? Also, Mercs have a softer ride (more comfortable for the passengers) than Beemers.
On the other hand, if your clients are slightly younger, then the Beemer might be a good choice.
Like you, I also contemplated the issue of professional image. I work as a consultant and have to visit clients frequently to do on-site work. However, in my case, I didn't want to give the impression of being too affluent, so I opted for the Beemer.
Of course the fun factor weighed in heavily on the decision as well.
Think of it this way, whatever the choice, it's still a pretty good ride.
Cheers!