long and short is you can't beat the go pro, the closest rival in terms of quality is the Contour+2, can't comment on the Bullet; never heard of them. My recommendation would be get the go pro as they are the most versatile of the lot; for example chest mounted, ski pole mounted, pistol grip, tripod mounted, helmet mounted, windscreen suction cup the list is endless.
If you don't want the go pro style then get a contour for the video quality over the noname ones.