I don't think you'll find a big difference in "impact repetition" between different brands. You give 'em a good whack, they should be replaced. More expensive helmets tend to weigh less (as previously noted), have better venting, better pads, and better retention systems (read: fit better). Proper fit is important, so make sure you get one that fits - obviously - but also one that is comfortable enough to be worn while properly adjusted. Snug, not too loose, not too tight.

As my wingman SteveDave sez: "Got a $40 head? Wear a $40 helmet."

Rg.