John,
Hard to say which is the best.........I've got two "guns" - a single action internal mix, and a double action gun - both are good for different uses.
I'd think your first step is to get a very simple, reliable, easy to use internal mix, single action airbrush, such as a Badger. Internal mix means the air/paint mixing is inside the body of the airbrush and the paint atomises just outside the gun, and the single action refers to the trigger - on or off for the airflow.
These simple spray guns have a screw assemply that allows the needle to move in or out, increasing or decreasing the paint flow through the gun.
If you have a proper regulator and airtrap on your compressor, it's easy to "fine tune" the output, therefore the paint application onto your model.
I can't reccommend getting an airbruch highly enough - the finish can be absolutely fantastic - and also a nightmare if you get it all wrong. It's somewhat frustrating at first, just experiment.
Finescale Modeler has quite a number of very informative and instructional articles on airbrushes, what's good and why, as well as articles on compressors. Have a look through the index for the month and year of the mag.
They also have a whole heap of articles on "how to" airbrush different types of models- everything from gloss paint for cars, to natural metal aircraft, simple to complicated camoflage for aircraft and armour.
We can go into this more in depth if you want to email me on leemitcheltree@bigpond.com
See ya,
Lee Tree