All of the brushes so far mentioned are good. You have to ask yourself what you are willing to spend. I would say get the best airbrush you can afford. Even if it hurts a little. If you have the opportunity to use different brushes before you decide on one it will help immensley. But I will say up front that there is NO MAGIC AIRBRUSH that works perfectly everytime and does not have its own set of quirks. Think of it in terms of fishing. All the equipment, boats, lures and baits are not going to make you any better a fisherman than the guy with a cane pole. Its how you fish that determines success.
Practice makes perfect and until you become comfortable and competent with it, practicing with it, experimenting with it and learning its action, all the money in the world won't help you. And you'll have an expensive straw from which to blow paint with. I'm not pointing fingers at anyone nor am I judging anyone, but how many of you guys sat down with your airbrush one day and did nothing but shoot water through it onto paper to detrmine the threshold of operation and to get the feel of the airbrush, practiced making lines, dots, shapes, tried distances and experimented, compared to how many of you sat down and loaded her up with paint, shot a few lines at the paper and then hit the model?
All airbrushes wear out. Needles, tips and caps are wear parts and need to be replaced dependent on amount of use, media pushed and maintenance performed. So there is no one time purchase.
Brushes are broken down into different catgories, external mix, single action needle in body, fixed double action, single action diffuser,indpendent double action and turbines. This does not include guns, sprayers and other specialty and different application airbrushes and guns. Just what you would likely need for models.
The two major differences that many here are involved with are single action and double action.Single actions use a simple air on and air off process. You manually adjust the paint flow for each application.Double action uses a valve and lever to adjust both paint flow and air flow, allowing you to perform different tasks just by moving the trigger back and forth and up and down. Everything is at your finger tips so to speak.
As for paint feed that is dependent on your own desire and what form of brush you decide on. Gravity feed cups have the advantage of easy clean, good paint flow, less work, but they use smaller amounts of paint and you must alter your work habits according to if you have a cap for the cup or not. 3D piant jobs will undoubtedly lead to some pretty weird hand angles. If your gravity cup doesn't have a cap you're going to paint your floor or bench.
Airbrushes are complex yet simple at the same time. Troubleshooting is not hard and usually only requires problem solving and an understanding of the mechanics and the ability to think through the problem. Sometimes not every fix works and that means a replacement. But that is part of this.
BTW Wingman....don't keep cranking it down, look for a gasket to make the fix. Air leaks out because there is a gap (no matter how minute)or at some point you crossthreaded the head. Try a new head, if that doesn't work then its the body. Last I remembered Aztek offered a lifetime on the body. Other problems with Aztek regarding splatter is simply because while cleaning the head the needle was inadvertently pushed up and damaged. This will cause it to sputter. Usually the last of the troubleshooting checks after all others have failed.
Other factors that you will have to experiment with are going to be paint mixing, thinner type, additive, air supply, mixing ratio, temperature, humidity, paint type, age, did it settle before you put it into the cup, does it have more pigment in it, how do you measure your mixing ratio. I personaly use a baby bird feeding hypodermic needle or horse syringes. This allows me to pull paint up from the bottle and acurately measure paint volume when mixing. Don't rely on looking at the "consistency of milk" if you want accurate and consistent results. While it no doubt works for some, paint in a 1 oz spray cup reacts differently than milk in a glass. Whole milk, raw milk, skim milk, no fat? all have different consistencies. Also milk does not have solid particles like paint pigment in it. So it will react differently. The more precise you can be the more consistent your results and the easier it will be able to match up your paint job if you have to go over it. Don't get me wrong its not that others methods don't work, because obviously they do. But they are not there to match their perceived results with yours. So what comparison can be made? What works for them is their experimentation and familiarity of use. You will have to develop your own and that means failure before success.
Don't expect it to do more than it or you are capable of. I've used quite a few models ranging from cheap craft store brushes all the way to big ticket turbo brushes. RIght now I'm using an Aztek and I like it. It's pretty versatile and I have had great success with it. Check out the Armour section and look for Panzer II photos. I did it with an Aztek. I've been interested in the metal bodied version that is released and that might be the ticket for that product line.
Good luck
Mike