I seem to remember that MCN did a survey on helmets sometime ago now and if memory serves me correctly they found little difference (in terms of safety) between the cheapest and the most expensive helmets. The advice was to go for the best fit according to your budget.
Personally Ive had quite a range including a cheap Lazer, Nolan, Shark and currently the superb Shoei XR1000, Ive never had an Arai. When I bought the Shoei the salesman did his best to sell me an Arai but it felt awful on where as the Shoei fitted like a glove. So I took the advice and went for fit and am very happy I did so its a great helmet and looks superb too.
Incidentally I binned my bike last year in France whilst wearing my previous Shark lid which took a heck of a blow and did a great job of protecting my head, a helmet I paid less than half for of my new Shoei!