My ideal camera would be somewhere between the two.
My initial thoughts are -
Contour HD Plus (only the plus has the external mic socket)
I like the mounting rail system especially for helmet mounting. It is simple to use, versatile and allows the camera to be returned to the same position each time. A friend who uses one has four mounting points set up on his bike, 3 forward, 1 rearward as well as the helmet mount. It's more than I'd use because his films tend to flip from one view to another too often for my liking, but regardless each mount gives good clear relatively vibration free pictures.
I like the slimline design of the camera. It sits in nice and close to the helmet without the tripod look of bits of mounting bracket sticking out at all angles.
I especially like the easy large slide on/off switch. It is easy to use with gloved hands and gives you confidence that recording has stopped/started without having to check. It also allows recording to be started/stopped while you're riding without groping for little buttons.
I like the idea of the Bluetooth connection to a mobile phone for viewfinding and changing settings etc
The GPS functions would be good for recording your favourite run, not so handy for touring but it could have its purposes.
The raw sound quality is very average and wind noise reduction is non existant. However as I said I would intend to use an external mic which gets around the problem.
I slightly prefer the colour accuracy of the Contour over the GoPro but that is more personal taste. The quality of both is excellent although the Contour seems to handle low light better than the GoPro. The GoPro seems to get grainy around the edges of the headlight beam.
GoPro Hero 2
The thing I really like about the GoPro is it's still and time lapse photography functions. You can produce some amazing effects with them and just gives the camera a flexibility of use that the Contour doesn't have.
It's slow motion function also appears superior to the Contour (120 vs 60 fps) although to a large extend good editing software can produce very sharp super slow mo's now a days.
I don't like that you can not attach an external mic while the camera is in its waterproof case (unless you drill a hole through the case), although this is only a problem if you want to use external mics which most people don't.
I like the suction cap mount itself, it is very sturdy and stable but I just find the whole mounting system for the GoPro a bit unwieldy and a bit like a meccano set. Apart from a tank top mounting, the Contour seems to be able to mounted anywhere the GoPro can in a more compact streamlined manner due to the rail mounting system.
In the end it comes down to personal preference and fitness for purpose. Both appear to be excellent cameras. At the moment I think I would slightly lean towards the Contour purely for it's overall ease of use; but I do like that time lapse function.
My first love was my motorbike, we went through everything together. Wind, rain, fences..