Hi
I started out with 35mm, moved to digital stills and have recently moved to video.
It has to be said though that I never classified myself as an underwater photographer, only someone who took pictures while underwater. Likewise I now wouldn't describe myself as an underwater videographer only someone..... well you get the picture. Based on that I have never gone for the high end gear. I used to have a Sea and Sea MX10, changed to a Sea and Sea DX3000 (Digital) and my video is a Sony DCRHC with and Ikelite housing.
Personally I moved to video for a couple of reasons
1. There are some things that you just cannot capture, or that it's very difficult to do justice to, on stills that look amazing on video. Glassfish in a cave for example. I must have taken hundreds of stills and its just a lot of little fish in a hole. On video I can capture the way they all move together and the way the light flashes off of them. It looks really good.
2. I find with video you can get good results from further away (only for bigger stuff obviously)
OK.... And it was an excuse to buy some new toys
There is a downside to video.
Basic video is more expensive than basic stills
You tend to be carrying a larger (and heavier) bit of kit
To get decent results you have to spend a bit of time editing, adding soundtracks etc whereas with stills you don't have to if you don't want to.