If you're looking for an air-brush compressor, there are a few things you have to consider. The first big question is to ask whether this is for home or professional use. Home use doesn't require the same dependability or rugged construction (and comes with a lower price tag) while commercial use requires better quality, these compressors will last longer under heavy-duty usage but come with higher costs.
Both home and commercial applications however require the same amount of airflow. Understand that the brush attachment doesn't know if it's a home job or a commercial job - all it understands is if it's getting the right airflow going through the nozzle. Note that your gun should tell you what airflow it requires to operate at the best capacity, and if in doubt, ask at the outlets that sold you the air brush.
And once you know this figure, experts advise to "oversize" that compressor at least a little to smooth out the demands. Remember you can always adjust or downsize the airflow to the brush if necessary. Note though that if you have a higher airflow, you can handle a thicker paint.
So what's important in air compressors? Noise is. This is particularly true when you're using it all day but even for occasional home use, you're going to want to muffle this baby. If a lack of sound is important, then look for airbrush-specific compressors. They are the quietest form of air compressor on the market but you'll wind up paying at least $1000 for this privilege. It is far cheaper to buy a compressor from a local box store and build a soundproof box around it.
You also require an oil-free compressor. Oil-less compressors cost more but you eliminate "fish-eyes" from your work with the miniscule droplets of oil put out by a machine lubed with oil. And the interesting thing is that oil-less compressors are noisier than similar oil-lubed machines. Oil-less machines run hotter without oil lubrication and they tend to have a shorter lifespan.
Water is a pain in the paint. All compressors spit water out the working end. This is a function of compressing air and can't be ignored. You will have to have a good compressed air filter at the working end of the line to remove the free water. If you are spraying onto a cool surface, you may inadvertently get some water droplets forming on that surface as water vapor in the air condenses. That being the case, you'll need an in-line air dryer.
If you're serious about using your airbrush compressor, you're going to want to install a good air regulator. This evens out the airflow and makes life a ton easier. It also enables you to lay paint with a steady flow rather than creating blobs because of uneven airflow.
A somewhat technical term "duty cycle" means whether the compressor is rated as continuous use or intermittent use. If you buy a compressor from a box store (mostly cheaper intermittent use models) do not expect it to paint an entire van side in one go without giving the compressor a rest, or you risk it burning out. They are not rated for long-term use rather they are better suited for filling up tires.
And those are the seven secrets of buying an air-brush compressor that you'll need to know.