I do not use gasoline that contains MTBE. It's an ecological thing. First, they told us it was better for the environment, then they found that it doesn't biodegrade, and has a tendency to collect in ground water. My choice eliminates Chevron, ARCO, Texaco, and Shell, so I use Union 76.
As for diesel, try to find out what the cetane rating of the diesel is that is available in your area, and use the highest cetane diesel you can buy. For Mercedes cars, the higher the better, as the diesel sold in this country isn't as high cetane as what is sold in Europe. The engines are designed with high compression ratios, and therefore, require high cetane fuel. That is why I always use Redline Diesel Fuel Catalyst, or Redline 85+ in my car, because among it's other benefits, it also increases the cetane of the fuel by several points. Diesel fuel does not contain MTBE, so I choose to buy diesel from Chevron, or Union 76. That choice is mainly based upon experience with diesel fuel quality during past cross-country operations of commercial vehicles.
"We drive into the future using only our rearview mirror."
- Marshall McLuhan -
Northern California Wine Country...
"Turbos whistle, grapes wine..."