The terms are often used interchangeably, but they mean different things. A clitoral stimulator describes what the toy is for, not how it works. Air-pressure vibrator and regular vibrator describe the technology. An air-pressure vibrator is thus a kind of clitoral stimulator, and there is also a small bullet vibrator that is held against the clitoris.
The real difference is the technology. An air-pressure vibrator has an opening that is placed over the clitoris. Inside the chamber, pulsing pressure waves are created, and the manufacturers describe the stimulation as touch-free: Womanizer writes that the air waves feel like a combination of sucking and soft pulses without touching the skin. A regular vibrator has a motor that shakes the entire toy, and the vibration is transferred to the body where the toy makes contact.
Neither of the technologies is better in itself. Air pressure is more targeted and requires less from you when it comes to angle and pressure, but it’s only used on the clitoris. A vibrator can be used on more places and in more ways, and comes in more shapes. There are also models that combine both.