Well, I'm 47 now, built my first model when I was around 7 or 8, took a break when I discovered girls at 15, started again when I was in my early 20s, stopped again when girls discovered me , and started up again a couple years ago after a 20 year hiatus. All in all probably only 10 years in all at the bench. Sorry to disappoint you!
I haven't owned the airbrush for that long though, it was a gift from a friend of mine who bought it new and used it to illustrate posters with. It might even be close to 30 yrs old. At least the handle and body is, the head assembly, washers and needle are brand new. Until then I hand brushed or used rattle cans. He gave it to me only a couple of years ago.
If I had to limit myself to one brush it would be the 100LG with the medium sized needle. I would also buy the fine head assembly and needle for spraying very fine lines, with very thinned paints.
That's a dual action brush, spush down on the trigger for air and pull it back for paint. The more you pull it back the more paint. It's a bit tricky, but once you get the hang of it, it works very well. You can save a few bucks and get the 200G with is the single action version. There you set the amount of paint by dialing the needle in and out of the nozzle, and push down the trigger for the airflow. The neat thing with this brush is that if you decide to upgrade to the 100 series in the future, all the parts are interchangable. The 150 is the 100 with a siphon feed. There is also the 150SF or Side Feed, which allows you to use the brush pointing straight down. It's very similar in use to a gravity feed, but has interchangeable color cups. It was designed for photo retouchers to use. It's pretty rare and many of the online shops don't bother with it.
In the perfect world of endless resources I would have the 200G, 100LG and 150, so I guess I'm two thirds the way to perfect! Right now I have the 150 with the medium head/needle and the 100LG has the fine head/needle. Oh, let's face it, I would have dozens of airbrushes: Badgers, Paasche, Iwata, T&C, Wold, Aerograph and many more. After all I would have endless resources!
Our very own MusicCity has an excellent article on the various choices of airbrushes.
It isn't so much what is a good beginner brush. It's all about practice, practice, practice and more practice. There are some people who are so talented I swear they could paint with a soda straw and their own lungs!