Go for something known & reputable (Iwata, Badger, H&S, Paasche & Grex come immediately to mind) - a good starting point would be a double action, gravity fed model with a medium nozzle needle combination.
If you don't already have an air source, keep in mind that a decent compressor will set you back as much, if not more than the airbrush. A compressor with an air tank would be ideal - CO2 is also worth considering.
I'm not saying that they are all bad, but many of the "airbrush kits" out there comprise either items of iffy quality, or have "stuff" included that you may not require, it's far wiser IMHO to ask the questions, narrow down your choices & get exactly what kit you want - that way you can shop around for the best deal on good kit without any miraculous "add-on's" that you may not ever use.