If you tons of light, the Silver is more or less as good. Not as many video modes, frame rates, resolutions etc, but for uw-video in general you will be just fine. The Black has sharper optics and less noise. So, if you bring strong video lights the Silver is good. If you don't you will be much better of with the Black. It is getting expensive though and you will probably want tons of extras, like display, battery, mounts, filters etc. My tips is to concentrate on big stuff and general uw feeling with the GoPro. And go for the smaller things with the G9.