This one.

The small hobby ones are nice, but to get a quiet one you have to spend big bucks. For less than that I got a huge 33 gallon tank so I never need to run the compressor while I'm working. (Actually, I had it already from my auto racing hobby. You can't run air tools from a little air brush compressor.)

I've wanted to try the little pancake 3 gallon compressors to see if I could do the same thing, probably could for small vehicles or for a squad, but then you'd have to run it. The little pancake compressors you can get from Harbor Freight or Lowes/Home Depot for less than $100. I think they are a better investment than a dedicated compressor for an airbrush.

Eventually I want to run an airline from the garage through the wall into my office paint station (they are adjacent). Then I can airbrush in the house and be far from the compressor.