A branded Gravity fed double action model would likely be your best bet.
Gravity fed airbrushes has a slight advantage over bottom fed as they can operated at a slightly lower pressure (they don't have to siphon the paint from the cup), this makes gravity more suited to detail work. Bottom fed brushes have the advantage of larger paint containers & quicker colour changes,.
On a single action airbrush, the trigger controls air flow only, paint flow usually being adjusted by a screw adjuster at the rear of the brush - adjustment is carried out when you aren't spraying.
On a double action airbrush, the trigger controls both air & paint flow, generally with a downwards movement of the trigger allowing air to flow & a rearwards movement allowing a variable & controlled flow of paint. Some double actions (H&S, Grex....) have continuous or coupled dual action, where the first portion of the rearwards trigger travel controls air flow & the latter portion of travel controls paint flow.
Some brands worth consideration; Harder & Steenbeck, Badger, Iwata, Grex, Paasche........... Have a scour about, read some reviews & if you get the opportunity try & get a demo, or at least handle what you shortlist.