I'm biased toward white helmets. If I was a fan of hi-viz, I'd wear that, but I go with white instead.

Your helmet is the highest piece of you that everyone else on the road will see, might as well wear a color that stands out and makes you seen.

I ride out west alot too in the mtns and there are many hills where you don't see anyone coming opposite direction until you're literally on top of the hill, so I want my white helmet to be in their field of view ASAP. A black helmet could just get lost in the shadows.