What is the best brand of gasoline to use?

The true way to answer this question is as follows: analyze gasoline samples from all the prospective gas stations in your area for a period of three to twelve months, then pick the consistently best gas.

In other words, this is an imposible question to answer. Gasoline quality and formulation vary enormously over the continent. Leaving aside race gas (100+ octane) there is no real way of telling which gas is the 'best' in your specific area. Just pick a high-octane brand and stick to it unless you have a problem.

For those unsatisfied with this answer, read the Gasoline FAQ (alternate link here), and seek out information from other local DSMers. Don't ask the Digest - somebody in California isn't going to be able to help you if you live in New York.