Consult the owner's manual for your car to find any required specifications for replacement headlight bulbs. After that, consider whether cost, brightness, longevity and appearance are the most important factors in your decision.
When you look at the packaging or product pages for headlight bulbs, pay attention to wattage, claims about performance and light output, the choice of high-intensity discharge or halogen bulb, whether the bulb complies with the U.S. Department of Transportation guidelines, and the price of a bulb. Customer ratings for bulbs appear on such shopping websites as Amazon.com, and they are a useful resource for determining the overall impression that different people have about each bulb you're considering.
Bulbs that give off the whitest, brightest light tend to be the most expensive, so be prepared to pay a bit more for that look. Bulbs that provide more light tend to last a shorter amount of time, because they operate at a higher intensity and temperature, which makes the bulb life shorter. High output bulbs tend to last about a year, but standard original equiopment manufacturer bulbs often last at least three years. People wanting the bluish white look that comes from an HID bulb may want a conversion kit to get the added brightness and intensity.