I'm late to the party here, but I wanted to throw in my 2 cents' worth. Are you locked into the GoPro line? I personally disliked the boxy outline of it on a helmet and wanted something a little less visible.
I watched a lot of YouTube moto videos and took note of what helmet cams were used. I ended up getting a very inexpensive
Drift Stealth 2 camera from Amazon. It's about $116 USD. (Update: I believe the Stealth 2 is out of production, although it's still being sold for about $80-$110 USD on eBay. YMMV.)
It has some issues: the rear hatch broke, so I have to be careful if it starts to rain. It's advertised as having a long-life battery, but I only get about 3 hours out of it. The audio quality is bad when riding because of wind noise unless you slightly mod it (by putting a cloth or a bandaid over the mic).
However, I love the streamlined shape and the picture quality is fine for my needs.
I've found that riding with a helmet cam is essential to me now as a safety issue in case there's an accident. I'm not interested in being a moto vlogger (where I ride and blather on to my legions of interested followers

). The Stealth 2 does great in low/no wind noise situations. If I'm in a crash, or there's a low speed issue (confrontation, etc), the camera is fine for my needs.
I'm thinking of getting an upgraded Drift or a Contour for my helmet and mounting my current one (with the broken hatch cover) on the rear of my bike to capture footage if someone runs into me. I've had two 'creeper' incidents recently, where I'm stopped at a light and the driver behind me is texting/creeps forward in his car. Scary. (My
$25 upgraded horn from NewBonneville was worth every penny.)
Go Pro is definitely the top of the line, I think -
Felix Baumgartner certainly thought so, hard to argue with his results, LOL.
It's a plus if you can get a camera that has easy-to-manipulate controls -- something you can turn on/off with a glove on -- or one that has a wrist-mounted or smartphone-operated remote control.
Good luck, and let us know what you end up getting. I love having a helmet cam.