I have a bunch of airbrushes, but the two that I use all the time are both Badgers -- a
105 Patriot, a real workhorse, and a
Sotar 20-20, fantastic for very fine work.
For a beginner, I'd highly recommend the Patriot with a fine needle. It's capable of fine lines right up to broad, heavy sprays, and it's very easy to clean and maintain, which is important. It's also relatively cheap, while being of excellent workmanship. Highly recommended.
The Sotar 20-20 is also easy to clean, but it's more expensive and is intended for much more delicate work. The spray aerosol is finer than the patriot will produce, and it will achieve much finer lines. Also highly recommended, but maybe not for a beginner.