There's so many brands and models that are good and available, and there are probably as many opinions about them, that such a question is impossible to anser.
But for most modellers, a gravity fed double action, with a medium size nozzle is probably the best.
Try to find and test a few before you decide. At least try them in your hand if possible.
Popular brands and models are Badger Patriot, Grex XG, H&S Evolution, Iwata Eclipse and Paasche Talon. All are good airbrushes.
Alternative, you might consider pistol grip airbrush. In My opinion, the transition from a single action to a pistol grip action may be smoother.