You need to have a high class rating on your cards otherwise they can have record issues. The Contour has a tough mount to deal with at the moment, usually mounted on the side, and it makes helmets kinda lopsided. The waterproof housing doesn't help this at all..
Can't go wrong with most class 10 cards.
Here is the aluminium mount that I put on my helmet for Go Pros. I know that it works much better than typical plastic sticky mounts, and I would highly recommend something similar for most cases.