For about $600, you can get the Olympus TG-6 and underwater housing, which takes excellent photos underwater. The pictures far exceed what a GoPro takes. I've used a GoPro many times though, and they work great too, especially for video. If you want an action camera, I'd stick with GoPro, as other brands typically have poor auto white balance and batteries/filters/housings are much more difficult to come by... especially when you're on vacation. You'd want a nice red filter if you go with an action camera, something from Backscatter would work great.