It depends on your situation but I really like my airbrush Iwata
HP-
CS.
How long have you been painting? The one thing I recommend is paint for a while before getting an airbrush since you will use a lot of the same skill you learned from painting with a brush.
I can now do a lot of things that was harder for me to do with a brush but which is still possible (i.e. gradient, etc)
It is a big investment but for me it was a good one