personally i hate the angle the go pro cameras create on the top of your helmet and i have witnessed a branch smash a go pro camera on the top of someone's helmet. i like the small profile of the contour and vio cameras. the contour is the obvious smallest with only the camera unit and no cables or anything and it still has the goggle strap mount which is best for skiing
both the vio and contour wash out when skiing into the sunlight, the contour probably worse, but that can be ignored or corrected with a homemade filter or (hopefully) an add on filter from one of the companies soon
i have a contour mainly because i didn't like the gopro quality or mount but i didn't want to pay 600 for a vio. the downsides are definitely wind, you can't hear shit, but just put music over the edit, and the lack of waterproofing. but it's super easy to center, stable, seems pretty strong, and light. it's more towards the level of the vio, yet only 100 bucks more than the gopro, so it's kind of a good compromise
i also think the quality and fps are better on the contour, it's just not quite as high performance for skiing. if you really care about wind noise and extreme waterproofing, spend the extra for the vio, but if you want a decent hd cam that's light, easy to use, and will hold up with plenty of snow hitting it as long as you're not swimming in it, get the contour
the gopro seemed like a good price point option until the contour came out, if bought in the right place, it's like 50 bucks more and a whole lot better