Claude - you really can't go wrong with any of the brushes you mentioned. Iwata, Paasche and Badger are all fine brands. You might want to check this out, a run down on buying airbrushes done by a member here (Music City)
http://www.craigcentral.com/models/ab.asp
Depending on what you model your airbrush needs might be different. If you mostly do armor a single action would fit your needs. If you do mostly aircraft, and have an eye for those snazzy German camo schemes with the squiggles (or think you ever might get a hankering for one) then a double action gravity fed would be the key...
Read around and come back and ask all the questions you want! A lot of people will tell you what works for them, from that and other online info you can make up your mind! Buyinf your first airbrush is about as frustrating as buying a new car!!! Hang in there and don't make any rushed decisions... the answer will come to you!
P.S. are you active duty or a federal employee? I did 11yrs in the Navy, mostly up there at sunny Bethesda! (I was a corpsman)
--edit--
check out www.dixieart.com, you'd be surprised how inexpensive an airbrush set is! dixieart is very reliable and shipping is free on every order over $45.00, which is almost any airbrush you can buy!!