I own the GoPro Hero 4 Silver [as well as a few of Sony's Action Cams]. For water fun and use, I use the GoPro, simply because I can see what the camera sees via an attached screen. With the Sony, i would need an additional accessory to do that [live view remote, LCD housing or a phone, but none can be used under the water]. I agree with the above, if price is not an option, GoPro is the way to go. They come with a few different backs...I believe one is a waterproof touch screen, which is just a thin plastic film over the screen area. the other is a hard plastic back: basically you cant use the touchscreen, but you are still able to easily start and stop recording. Using this one also allow you to dive deeper [forgive me but i forget how deep, something like 13 feet maybe?
I hope this helps!
Enjoy and KUNGALOOSH!!
Brian