Airbrush supposedly looks more natural. I found this explanation at airbrushtouch.com:
Airbrush makeup is sprayed on through an air compressor as a fine mist of color that gently covers the skin, giving the appearance of a flawless complexion. Spraying microdots of makeup that rest on the surface of the face looks more natural than traditional makeup because it isn't rubbed into the skin and doesn’t exaggerate the pores. This process allows the Airbrush makeup to conceal better while enabling your skin to breathe.
Traditional foundations can look obvious, caked-on or thick and always feel like you are wearing makeup. Airbrush makeup leaves a light, seamless veil of color over the skin, creating the illusion of a perfect face because it is misted on, allowing your true skin tone to show through without masking your face. The ability to mix Airbrush foundation colors for individual custom blends is unsurpassed, resulting in a more natural look that covers skin imperfections effortlessly.