You can get them with image stabilisers? If it's a helmet camera your neck should absorb all the vibrations anyway and if you mount it on the bars, your mount should have rubber or something to dampen the vibration there.
Gopro is a pain for a helmet cam due to its profile. It will create wind resistance and therefore drag and pull your head back.
I have a Drift HD170 which I've recently changed from bar to helmet mount and it's pretty damn good. Ensuring it misses your speedo (and avoids too much sky) is easy as you can tilt it on the mount and the lens is rotatable to align it perfectly and get the image straight.
There are now smaller drift cameras but the way this one is shaped means I get no wind noise from it. The downside is the large battery is a definite requirement if you want it to last a few hours (3 or so) and it takes ages to charge.
The Contour ones are smaller which is a defo bonus but as I say, the larger Drift HD170 is pretty damn big and fairly heavy but I don't notice a difference mounting it on the lower part of the side of the helmet.
If you're thinking of using it for "Vlogging" then you'll need a mic separately as the external one will just pick up wind.
You have to be aware that if the camera is found by the cops after they suspect you've been riding silly, they can and will take it as evidence. Avoid your speedo as if it captures it, and you've gone over by only a bit accidentally you'll have a hell of a time. Even though you can show that the speedo isn't calibrated and therefore hopefully inadmissible as evidence in court. Also, in an accident it will show the whole truth and nothing but.
You can get ones for £50ish but they're nowhere near as good. If you want an idea, have a look at a few of the motorcycle "vloggers" on youtube. They usually say on their channel what set up they use. If I were getting another camera I'd be happy with the Drift ones. The lenses are also replaceable if they get damaged which is very handy. They also do a mount which will attach to an RIS rail on an assault rifle.