I've done decades of MRR modeling, and all manner of painting...from weathering, to full paint jobs, etc...on them with an airbrush.
First, I absolutely agree with lordjw in one respect. Metallic 2-action airbrush with a top feed cup. The cheaper plastic airbrushes WILL fail, sooner rather than later. Yeah, the metal dual action brushes are a bit more expensive (though not THAT bad if you can haunt e-bay for a few days), but worth it. Correctly taken car of, they'll last for YEARS (my Paasche is 8 years old and works flawlessly) where, ime, the plastic testors ones will last months if you're lucky.
Personally, I happen to think Paasche airbrushes are the best in the world, but PLENTY of manufacturers make quality metal brushes. Badger, Model Master and Tamiya all make good ones. The Model Master/Aztec line is especially popular amongst model railroaders.
I must, however, disagree with lordjw on one point. IMO, "any compressor" is not fine for model painting. I strongly believe that compressors are a VERY overlooked component of an airbrush system. Ignoring the quality of compressor is, essentially, like ignoring the stability and quality of the power supply to your race track.
Personally, I happen to think there are two brands of compressors on the market. Badgers, and the ones that don't work well.
Again, a bit pricey at times, but long term worth the investment imo.
HTH!
/gb