Chest every time! Much more interesting with your arms and bars in, than what appears to be a flouting camera on the helmet!
Take a look on dx.com, loads to choose from and way cheaper than the official GoPro stuff!
I got a aluminium bar mount which i use to mount to my seat post and forks (with a bit of inner tube) for like £3! with those sort of prices, you don’t mind buying and never using!
Think about a fork mount as well. I have a shoulder mount and a rear-facing mount near the rear axle, & am going to buy a fork mount next.
Wheel-angled shots give a great sense of speed & ‘lean’ & mixing up the viewpoints in the edit makes the vid much more interesting (mine are still dull but not quite as dull!)