I'll second all the info about different manufacturers building to different head shapes. I will also second the previous comment about HJC. I used to have a REALLY expensive ARAI (motorcycle) helmet that never was comfortable. I got an HJC with a bike that I bought and have owned nothing else since (for motorcycles).

I have a G-Force racing helmet that is very comfortable. Does anyone know who sells HJC SA-rated helmets? I'll need to replace mine soon and would not hesitate to get an HJC.