To get right to the point of my writing: I can't give you a definite answer. What I can definitely tell you right now is that we are to focus on the GoPro HERO4 and HERO3+'s (and I will touch base on a few HERO2 and original 3's as well), as it is the best technology and provides options for numerous consumers. With the recent announcement of the HERO4's especially, we'll tackle the main features of those to help you decide if that hefty price is worth it.
The GoPro Hero 5 is a fantastic underwater camera. However, there is a catch. The device cannot submerge on its own. Rather, it requires a Super Suit Dive Housing (also from GoPro) to get wet. Even so, that accessory turns it into one of the best diving cameras around. The device is able to go down to 196 feet and comes with a bright 2-inch touchscreen display that is easy to use while swimming. The ultra-wide angle lens, 4k recording capabilities, and 12MP image resolution bring it all together.