I've had consistently excellent service from
Chicago Airbrush Supply, and their prices are great — plus, they have regular sales when everything gets even cheaper.
I have a Badger 150 (double action, bottom feed) that has done sterling service for nearly 40 years. More recently, I bought a couple of gravity-feed brushes — a Paasche Talon (double action) and Badger 200GF (single action), both of which are excellent brushes, and a bit easier to keep clean on the run than a bottom-feed brush.
The single-action Badger 200 is probably easier to manage for a beginner, and is capable of nice fine lines as well as broad spray patterns. A double-action brush is going to be more flexible in the long run, but will also have a steeper learning curve.