I've gone through 4 different brands of airbrush in the 25 years I've been modeling, and Iwata is the best overall performer.
The HP-BCS is a great brush for multi-tasking, spraying large areas or doing relatively fine work. If you're doing helmets, tanks, guitars or vans (yup, done them all), then the BCS is perfect. The HP-SBS is also good if you're using heavier paints.
If you want super-fine details, the Micron C and C+ are the way to go. They're expensive and sometimes fussy, but you can spray a 1/16" line with no troubles whatsoever.
I currently have 4 Iwata brushes that I use on a regular basis, an HP-BCS, an HP-SBS, a Micron C+, and an HP-SB+. Each has a specific use and I try to stick the brush that performs that task best. My Badger, Paasche, Binks, and Aztec haven't seen the light of day in nearly 10 years.
Don't try to find a brush that will do everything, it's simply not out there. You can find some great all-around brushes, but in the end, if you're looking to do specialty work, then a specialty brush is what you'll need.
Above all else, airbrushing takes talent and practice. I'm not talking about spraying an ambush scheme on a tank model, I'm talking about motorcycle tank art or helmet art.
A good brush and a good compressor should be looked on as an investment. Spending more money on them will make a definitive difference in the long term.
Jeff