Aztecs seem to have more problems than benefits, though some swear by them. I've never used one. Asking which airbrush is best is like asking which car is better, Chevy or Ford? (the answer is Honda!).
You have a lot of decisions to make: Single vs. dual action, siphon, side or gravity feed. Enamel vs. acrylics, etc. etc. A good place to read up is Music City's website http://www.craigcentral.com/models/ . After you've picked your jaw off the floor from looking at his aircraft, scroll down and read up on airbrushes, paints and sundry tips. Make sure you bookmark the site so you can refer back. Another good site to bookmark is Swanny's http://swannysmodels.com/ yet another jaw dropping site with many great tips.
All that being said, I use a Badger 150 with an ancient compressor a friend gave me, and I spray acrylics exclusively. I can't stand the smell of enamels. I-beam's setup is pretty sweet. I'm thinking about upgrading the compressor to one like his (it would come in handy since I'm renovating my house), though I think I would buy a longer hose, they're not exactly quiet! . I have a pretty nice (if I say so myself) spray booth http://www.finescale.com/fsm/community/forum/topic.asp?TOPIC_ID=48843) which has had a turntable, lexan doors, pressure regulator and moisture trap added to it since those photos were taken.
Good luck with your decision!
Oh yes, and
to the forums! Pull up a keyboard and stay a while.