they all have to got hrough a ratings process to be certified so they are all pretty similar in protection. the only difference is with bern. their helmets are certififed as "hard-hats" so i guess they dont provide as much protection.
There aren't really any, "all-mountain" or "park" helmets. There's just mainly different styles, though some of the newer helmets use Brock Foam instead of EPS, not that Brock Foam is inferior or anything. Brock Foam actually protects your head better, but is not as tough against massive impact. I have a Bern helmet and love it simple because it's warm and very comfortable.
The process of getting the brock foam helmets certified is a long and expensive one. They should release some figures, but I am super anal about my head (please no siglines :P) but it seems like it will work out fine.