I've looked at many videos shot with a Contour HD and GoPro Hero HD. Both videos look about the same in quality in terms of capturing images, blurriness, focus, etc.

Colour saturation is better in the GoPro Hero HD.
In some videos Contour HD seems sharper. Still others, GoPro Hero HD shows better sharpness.

Sometimes the distorted fisheye effect of the GoPro Hero HD doesn't give as good an image at the fringes (edges).

Both are capable cameras. I prefer the Contour HD for helmet. I don't own the GoPro, but am considering getting one. It would be good to get a mixture.

Drift is also (has also) released a new camera that is the same as the 170 HD, more or less, but improved, and is 25% shorter.