The fit varies by manufacturer. I just bought two new helmets this summer, to replace my Giro Pneumo helmets. I found that Bell. Bontrager and Louis Garneau fit me fine, but Specialized didn't fit comfortably. I didn't try any Giros this time around because I wanted something with big vents and a removable visor, and they don't make any like that.

I would up buying a Bell Volt, which is generally comfortable but I find that the straps are very stiff and they tend to irritate my ears. Still I'm able to wear it on my long weekend rides.

For my second helmet, which I use for evening rides, having a visor isn't so important to me so I got a Bontrager. I don't remember which model. It was one of their mid-range models, not cheap but not the ones the pros wear either. (And the straps are nice and soft.)