This is some of the best discussion of motorcycle helmets and testing I have seen anywhere. It certainly made me rethink a lot of my assumptions.
Basically, do you want a tough helmet, or a soft and squishy one. I’m thinking soft and squishy is probably best.
Here is the testing and analysis http://motorcyclistonline.com/gearbox/hatz/
And here is a more general discussion relating to same, and links to heaps and heaps of resources. http://www.webbikeworld.com/motorcycle-helmets/motorcycle-helmet-faq.htm