I have always used Shell V-Power, with good success on my last 3 S4's (2000, 2001, 2004).

Is there any comparison done between that and Chevron Techron? I tried techron a few times and wasn't particularly impressed, but didn't use long enough to notice any cleaning benefits. Never had an issue in the S4 4.2L engine up to 60k + miles when I sold. Never had carbon cleaned but pipes got sooty, and it progressed in severity beyond about 45k miles. Of course 45-55k miles was winter driving too, maybe additives make a difference? I am no gasoline expert.

Also bad, no-name fuel, racetrac, etc.

Exxon and Mobil are fine, but I prefer Shell and Chevron.

light. Code read multiple misfire. Cleared the code and filled up with Chevron and all is good so far. No soot whatsoever on the tailpipes.

isn't that what some claim here?

Any tier 1 premium grade is okay.

it's a mex company.