I ran a gopro HD in the past, currently running 2 Contour Roams. I'll try to break down my likes/dislikes about each.
ease of manipulation while riding (I can turn it off/on, and know if its off/on just by feeling for the position of the switch)
shape seems to create less wind noise, and less drag when mounted on the helmet
you cannot change settings 'on the fly', as it requires a PC or multiple microsd cards with the appropriately modified config.
I have yet to find a way to dump the video from the camera, without the camera. The microsd card does not contain a partition table or some other silly shit that keeps it from appearing as ready to use. User error may be at play here. I'm not a newbie to Linux, but sometimes it does shit that I don't expect.
Can change settings "on the fly", but requires a friend unless you are stopped and willing to wrestle it off of your helmet...easily averted by memorizing the beeps/menus for navigation, but you still have to slow down enough to hear it.
Better camera, removable battery pack with battery backpack option.
My first one failed before the year was up. The replacement failed within 6 months.
Without the case, there is (to my knowledge) not a way to mount it.
If your concern is video quality while riding, check out this video. Getting pulled over, for supposedly doing 40 in a 25mph school zone - YouTube
It was shot in 1080p, so you can play with the resolution to see the difference. Most people will be viewing this on a small screen (e.g. not a TV) so the difference is hard to distinguish.
I don't have any 1080p gopro video posted for a comparision, but there is plenty out there.