Which GoPro should I purchase?

So, I really want a GoPro for my vacation to Cancun this summer! And I am getting really overwhelmed with information. I don t know which to get with all of the different options. If I had a ton of money to spend, I d obviously go with the newest, but that isn t the case. I would not like to spend any more than $200, maybe not even $150… Because I know I will want to buy accessories. I plan on using it throughout the days, so a good battery life is important. We re probably going snorkeling so good underwater image quality is important. I love photography, and have a DSLR camera… But I want to venture with action video, so something good quality, but cheap and accessible! I was originally thinking the original Hero, then was considering the newer Hero Session… Or maybe a Hero3? I have no idea you guys! Please help me figure this out. Information overload over here haha.

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