I've been ab'in for one year now, and I'm by no means an expert. You will find many here, so you just have to wait for a probably better informed response.
That said, in my experience and opinion, that greatly depends on your budget and your expectations regarding airbrushing. If you plan to make just basecoats for those boxes, I would say your best shot would be going chinese: they are inexpensive and work fairly well. Probably no brand/model can beat their price/results. They will work well also for not too detailed work, using stencils to paint a fixed and simple pattern and things like that.
If, on the other hand, you plan to make more use of the airbrush than that; that is: fine decoration, illustration, painting tshirts in you free time (or profesinally), helmets or whatever, then I would suggest going for something more reliable and precise. In the cheap side of things you have the Krome, which is an absolutely wonderful airbrush for the price. I own one and it's a pice of gear. Anyway, there are many more questions left. Depending on the throughput that you want (number of boxes a day to be painted with the AB) you could do using a siphon feed, or a touch-up paint gun, which can hold much more paint than the regular gravity feed airbrushes (the krome for instance, is a gravity feed one).
In between, with great quality, not so much for detail, and a little bit more pricey in the rank of price/quality, I would REALLY recomend the Iwata Eclipse (HP-CS), that one is cheap among iwata (iwata parts can be really expensive, but this line is cheaper than most of the others), and is smooth, easy to use and clean, forgiving, hard as a rock... a real workhorse. I own one and it's probably the most trustworthy airbrush that I have. The thing of Iwata is that I find it somehow easier to handle (cleaning, taking apart...) than the others. They have super smooth paint cups, which makes them easy to clean, and they give the overall impression of being built by people with great attention to detail (i.e: Japanese guys)
