Air flow is not that important unless you are climbing mountains on really hot days.
Just try on a bunch of helmets and buy the one that fits your head size/shape the best.
Also, look for adjustments that are easy for you to understand. Most helmets have adjustments on the sides and back, as well as the neck strap. Carefully adjusting the helmet should prevent it from falling off your head during a crash.
All helmets sold in the USA have to meet minimum safety requirements, so even a cheap helmet will work well if it fits you well.