I ended up getting the Contour +2 to replace my contour HD for the underwater housing and other features.
You should just look at the specs and see what you need/want. The GPS is mainly useful when viewing in storyteller (their software) or when you upload to their site. Otherwise it isn't usable by other video editing software
for the most part. Do you want a wide angle lens or are you not as concerned - the wider lenses on the newest cameras do have some fish
eye, but I don't find it to be an issue.
You can see a couple of videos I posted with the +2 here : Contour | Users | maytrix
And some older ones with the Contour HD 1080P here: TweedValleyTravelers's channel - YouTube
Haven't uploaded any boat footage yet.