First, make sure your brake rotors and pads don't have oil or grease on 'em. That can cause some issues. A bit of brake cleaner on them solves that problem nicely.
That said, I've used the following brake pad brands with good results on M-B's:
- Ate
- Bosch
- Pagid
- Akebono
The key, I've found, is to actually use that brake pad lubrication paste that they usually include. When I didn't do that, my Bosch pads would squeak mightily loudly when I backed up. So, lesson learned on that, and I've done it since with quiet brakes.
All three brands have given good stopping performance for me. The biggest difference that I've seen is how much they "dust" the wheels with brake pad particles. This may matter if you've got really nice wheels and want them to stay looking cleaner for longer. Ate's and Pagid's do tend to "dust" on the wheels a bit more than the other two I've used. The Akebono's put out the least dust, by far. The Bosch's dust a little bit less than the Pagid's, but not much less.
If you're just looking at straight stopping power, then for the money, I'd go with Ate's or Pagid's. They're usually the least expensive, generally, and they *are* Mercedes-Benz OEM, so you're good there.
Make sure your rotors are also in good shape. I tend to use Brembo or Zimmermann rotors, since they're M-B OEM. I did try out Meyle rotors on a 2000 S500, and even though they're "made in China", they actually do pretty well; I was pleasantly surprised. But the OEM ones cost close enough to the same that I go with those now.