I have used the Contour HD 1080, and recently got some other stuff that I will talk about in a moment. I am very interested in the Replay 1080 (The R7), but the biggest problem is that it does not have a removable battery. So you are limited to the two hours of battery time. But it is very easy to use, and durable. I have not used the GoPro's, but they seem good enough, with the only issue being that a frontal size is big, and the mounts are a bit obnoxious (Like you can mount in on top of your mask, or the variations to mount it on your barrel are big). With the Contour, you get a smaller frontal size that can mount on the side of your mask, of with a bit of small work, you can mount it on your barrel. The nice thing with the GoPro and the Contour is that you can replace the batteries, so you film for a couple of hours, and swap the battery, and keep filming.
Now, for an alternative, there is the Midland XTC 300. This is very similar to the Contour Roam, and very easy to use. It uses the same batteries as the Contour's, and for $250, you get everything that the Contour would come with, other than a memory card, and a bit more. It even includes a waterproof case, which is important in that the body of the Midland is plastic, not metal like the Contour.
So just a few thoughts.