Once you try Arai, there's no going back... 8-)
I used to wonder what the fuss was about them in the mid-80s until I tried one on at the BMF and thought "Aaahhh, now I get it", bought one and have worn them ever since, now on my 11th (12th if you include the off-road one as well)
Like Lis says, it's a very personal thing, you have to get what you really like and are comfortable in, and it'll be the bit of kit most responsible for keeping you alive in the event of a prang :'(
I like the old saying: "If you've got a ten dollar head, get a ten dollar helmet!"