While it may seem intuitive that more expensive gas is the better choice for any car or truck, the reality is that the best gasoline for any vehicle is the one specified in the owner's manual. Paying more for a higher octane may not produce any benefits at all.
The octane rating of any fuel describes how hot it burns in a combustion engine. Most standard-grade gasoline in the United States is 87 octane, while mid-grade is usually 89. Premium is usually 90 or higher. These designations have nothing to do with the quality of the gas, and most brands contain identical detergents and other ingredients in each grade of gasoline.
Octane can play a factor in an engine's smooth running. When fuel does not combust properly, it can disrupt the engine's natural cycle and cause knocking. In most cases, an engine runs fine on the fuel it is rated for, and modern vehicles have anti-knock sensors that adjust fuel flow to prevent this problem. However, some older vehicles that begin to experience engine knocking may benefit from a slightly higher octane gas. However, this is a temporary solution to the problem, and any engine knock should be diagnosed by a mechanic to prevent further problems.