960p has a good aspect ratio for helmet cam shots. however, i highly advise you to keep a single size and aspect ratio when filming. 720p and 1080p have the same aspect ratios (16:9), so it's possible to film in 1080p and conform to 720p, making the footage look the same. why do it though, if you know you're making an edit in 720p? also never conform 720p to 1080p, you'll lose quality. don't even bother mixing 960p footage in there either, the different aspect ratio (4:3) will either put bars on the sides of the video (unconformed) or make the image short and fat (if you conform it).
TL;DR: you can film in 1080p and conform it to 720p, but not vice versa. don't mix 960p and 1080p or 720p footage.
720p60fps wins