Your vehicle's owner manual and gas cap says to use regular unleaded. Will you get better mileage and results by switching from regular octane to midgrade or premium fuel?
The short answer is no. If the vehicle was designed to run on regular unleaded, the only thing you'll notice by using a higher grade fuel is that it costs you more to fill up your tank.
The only time you will likely notice a performance change is if your vehicle requires mid-grade or premium fuel and you use a lower octane rating than recommended.
Without getting too technical, the octane rating is determined by the compression ratio of the engine. The higher the compression ratio, the higher the octane rating and higher ignition point needed to get a proper fuel burn. If you cheap out and use a lower octane rating than recommended, you'll notice knocking and pinging from the engine, which is the fuel burning too soon. Other than the noise and possible reduced power caused by using a lower-than-recommended octane rating, you'll risk overheating your engine because of the uncontrolled detonation.
The only exception to this rule comes for those of us driving in very high altitudes, such as in Denver, Colorado. At those high altitudes, regular unleaded is 85 octane, not 87 octane. In those areas, if your vehicle calls for regular unleaded, choose the octane rating labeled "regular" on the pump.
So don't fall for advertisements that cleverly suggest that mid-grade or premium fuel is better for your car if your manufacturer recommends regular. Just use what your manufacturer recommends. It's not worth the added expense and won't boost your fuel economy.