As long as a helmet meets the standard you want it to (DOT, Snell or whatever) then it's more a question of a) what fits your head and 2) how much do you want to spend.
Arai helmets come in small variations of inner shell shape, depending on which market they are being sold in, since human heads vary by ethnicity. Feedback I have received from friends who wear them is that you either have an Arai shaped head or you don't. Each helmet is apparently virtually hand made using the best components, so you pay a premium.
In my opinion, the myth of Arai heads or not is just that, a myth. I nearly guarantee that there's an Arai to fit your melon. In the US, there are three Arai head shapes: long oval, round, and in between. You just need to find the one that's right for you. For me, when I wore an Arai, I first had an improperly fitted Quantum (round). Then I was fitted, and was told to try a Signet GT (long oval). It fit wonderfully. I then replaced it when it was time with another one. The Signet has since been replaced by the Profile model. The Astral is the in between shape. Arais are VERY nice helmets. They are very pricey though, and can only be purchased through dealers... no mail order. They do that so you buy a helmet that fits.
Shoei has helmets in various shapes as well. The RF series are roundish and fit my head poorly. You may have a round head, so it may fit you. The pricey and very nice X-11 are long oval, but not as long as the Arai Profile. These were close to fitting my head, but not quite right. The Shoei TZ-R is long oval, and fit me perfectly. It's a comfy helmet, and mine, being flat black was a bargain compared to the Arais and the X-11 at under $300. The downside is the interior isn't completely removable.
My biggest recommendation is to go to a shop and try alot of helmets on. Walk around the shop in them... get a feel for them. Sometimes lids will feel good at the beginning, then you'll get a headache after 5-10 minutes. They aren't fitting right. Measure the circumference of your head, above your ears and about an inch above your eyebrows. That way you'll know what size to try. Don't just buy another size larger if your suggested size doesn't fit right. That means it's not the right shape, and if you go up a size, the helmet will move at speed, be really windy and just plain annoying. Some people will suggest compressing the foam at your forehead with a spoon to get a helmet to fit right. Don't do that. You'll be compressing the foam that's supposed to take the impact, rendering it less effective and your head will take the forces instead.
FWIW, I bought a Shoei instead of another Arai because we don't sell Arais where I work, but we do sell Shoei. If we sold Arai I probably would've bought another.... but I'm not 100% sure.
If my long winded drawn out reply isn't enough (sorry, I like talking about helmets), be sure to read this article from Motorcyclist Mag.
http://www.motorcyclistonline.com/gearbox/motorcycle_helmet_review/index.html. It's a good one.
Hope this all helps.
Jeff
