I have found that 76 premium seems to work best on my car, it really adds alot of power.
It is more expensive than other fuels but worth it in my opinion

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1996 E320
2000 C230 Kompressor
1988 190e 2.3 - 225K miles, owned for 7 years. I cannot say enough good things about this car. Very well built, even at 225 it ran like new.