your pick. top or side of helmet. I have two mounts on my helmet (top and left side of helmet). you may need to test (while taping it to see if you got good visibleable) on where you want to mount it before you peel it off then put it on.
I have a gopro hero 2 and other one is hero 1. The different between of 1080 hd, hero 2 is better than hero 1 but have not tried it on snowmobile yet (no snow here in iowa). If you want more wide (top to bottom, side to side), switch into 960. I like 960 on my hero 1, have not tried 960 on hero 2 yet.