I've been filming my trips for a few years.
1. Helmet cam is the easiest and good if you have a few passengers on the front for a good perspective. Also, you are always looking towards the dangerous/scary stuff, so you end up capturing it on camera when someone flips.
2. Hiking pole mount. Great if you have a passenger who is doing nothing, you get all kind of angles and perspectives. Can't do it if you are solo in the boat.
3. Helmet camera reversed to capture the captain. I did it with two helmet cams, mine was looking forward and my passenger was looking back.
4. Tripod mounted on the stern. I've seen various mounts. Some are self made, some are tripods. I use a cheapo ebayed tripod. When I break it, I just buy another one for 20 bucks. Just what cataraftgirl said, make sure you put a tether line on the camera. I already lost one GoPro in Westwater when my boat flipped and tripod broke.
5. We also tried oar mounted camera, but it didn't turn out well.
6. Bow mounted looking forward is probably the least entertaining to watch. A lot of videos on Youtube are of the front passengers holding the cams and all you see is waves. You have to have something in the picture for the perspective and show the size of those waves, otherwise all you see is splashing.
7. just what h2obro said, multiple angles usually get the best footage overall
Hope this helps,