I own 4 airbrushes (Masters G44, Iwata Neo, DeVilbiss DAGR, Harder and Steenbeck Infinity) and would not get a spraygun unless it is a professional quality and really need to base coat some very large items.
http://models-workshop.com/buying-a-new-airbrush/
There is a tutorial I wrote and then did a video for. Should answer a lot of basic questions in regards to airbrushes.
For a basic rig as a beginner I really recommend the Master G44/G43. More advanced brushes, do research. If you have the cash a good Iwata or Harder and Steenbeck is the way to go.