Typically, this is the part where I would say something like "GoPro's only real competition is itself." Of course, there's the Sony Action Cam line, which has some dedicated followers but isn't quite as versatile as a GoPro, thanks to fewer mounts and the slim-but-tall form factor. There's now a new rival from DJI. I already thought the Hero 7 was a better overall camera than the Osmo Action, despite strong competition on the stabilization front (and that second, forward-facing "selfie" screen). The Hero 8 just makes that decision a little clearer.
The reason I ask what you will be using it for is to determine which set of features you need. If you're going to be using it for simpler activities, don't go all out for a Black edition with a 60fps, 1080p cam (all HERO3's are 1080p, anyways). The reason the Black Edition is so expensive is because of the crazy quality it has, and if you're using it for a more simple basis I wouldn't worry about the difference. The Silver or even White is perfectly fine for you. The main difference between these two is the white's camera has a 5 megapixels with 3fps burst while the silver is 11 megapixels with a 10 fps burst -- is that worth $100 to you?
Some GoPro cameras have user-replaceable batteries, and some don’t. If you need a camera for camping or several days away from home, you’re going to want the former. If you buy a GoPro camera with a swappable battery, you can keep extras with you, so you’ll never miss filming the perfect moment. On the other hand, if you’ll only be using your camera for an hour or two at a time, you can save money by getting a model without a user-replaceable battery.

best underwater camera