Choosing the right Iwata for fine lines would depend on how much you are wiling to spend I guess. I purchased my HP-CR for around $65, and it is quite capable of producing fine lines as well as overall coverage. Then there is the other end of the spectrum with the Micron CM-C which I've seen for $330! but that model is supposed to be able to spray very fine lines.
Although I have never used them, I have heard nothing but great things about the Badgers, so it may come down to price or whatever AB feels most comfortable in your hand.