I'm very new to airbrushing, but started with Vallejo Model Air paints. They work very well, but for lower pressures I had all sorts of problems till I thinned them even more and also added a retarder. Medium-high pressure (15-18 psi) for broad coverage with the base color coat and pre-decaling with the gloss clear worked just peachy right out of the bottle.
I thinned the cammo and top color coat paints about 50% from the bottle. That 50% was made up mostly of the Vallejo thinner (basically super thin clear coat, as it contains acrylic resins for maintaining the bonding), a few drops of Flow-Aid water, and one drop of Golden retarder. Mixed well, as the retarder is a gel. I'd get virtually no clogs that way even at sub 10 PSI pressures. Be advised that I did have to increase the thinning for the really dark colors... RLM 82/83 took a bit more than 50%.
The Vallejo thinner works well but is very expensive for the volume you get vs. how much you wind up using. I'm going to try some different brands of airbrush medium / thinner that contain resins that you can get at Michaels in large quantities for a fraction of the price per ml. Using nothing but distilled flow-aid water with Model Air resulted in some very weak looking finishes... multiple passes fixed it, but it ran/spidered much, much easier with water thinner vs. Vallejo thinner.
The bottles are awesome, and so much easier to work with than constantly cleaning droppers for use in the little jars.
Avoid the large kit collections of Model Air you see Amazon et. al., as the price per paint bottle is really elevated. SciFiGenre has a huge selection for just under $3 a bottle, and Sprue Brothers carries them for a few cents more. The color fidelity of some of the RLM colors seems a bit suspect when compared with the RLM paint chip sheets in several of my reference manuals, but of course who really knows what the exact hue of any RLM color was at any particular day/month of the war.