Focus more on whats going to be best for you, rather then the definition etc.
I bought a GoPro, which is shithouse (ok, it was good, but not HD, and especially with the sounds, only hearing wind that they apparently overcame) for karting. It worked well on a supermotard for some reason.
Something that would create minimal drag would be good, though if its going inside a vehicle then you have to worry about hearing the engine more than anything. The GoPro video qual was excellent in my Subaru, which mind you was extremely loud with a sports exhaust and carbon fibre air filter to briefly list, yet i could hardly hear the engine, all i could hear was clicks and rattling from the movement.
Point is, focus on setup, what's the best to setup for your needs. A HD camera that would wobble here and there will give you the worst quality ever.
PS, i wasnt happy with the GoPro one bit, and the videos that you see on their site they had to have been using a different camera.