Whats the difference between the different versions of GoPro cameras?

I need a gopro, one thats waterproof (that I can take to the pool) and takes good quality videos. I dont really care for the latest one that much, I just need a cheap fix. I'd prefer it to be brand new, I'l probably buy it from Best Buy. Whats the difference between the Hero 2-Hero 5? And the other ones as well? Thanks!

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