I use a single action Paasche airbrush, an H # 1 model. The simple, easy, and least complex tool out there. It’s the VW Bug of airbrushes. Single action refers to the button you push on the top of the airbrush to get a spray. The H#1 is the easiest, you push down, all the while controlling the needle or aperture size. A double action airbrush you must use 2 finger movements , push down, and pull back to control the air supply and stream of paint, ink etc. Of course you can get a little more control in the double action, but for a beginner the single action will be a lot less frustrating!
It really depends on what you are painting. I use acrylic paints to spray thru mine, more about that in lesson # 4 . Depending on the size of the piece would have a bearing on the tip size you want to use. When I am needing a lot of coverage quickly on a big portion of the canvas, I would use a # 5 tip. This gives you a large aperture to open up all the way and spray for coverage. Obviously you wouldn’t want to use this tip for fine detail. It’s good to have at least 3 different size tips that you can inter-change to suit what you are painting.
48 x 60 Sean Tomson wins the Pipe Masters
Honestly, I’d start out with a single action it is a heck of a lot easier. I always taught my students on a single action, they were much more interested in seeing what the airbrush results were….immediate gratification! You can find an H1 Paasche set with the airbrush, hose, a couple of tips, and bottles around $90. I suggest using their H-Set pkg. to start out with.