LOL ask this in the video section and you'll get lots of VIDEO! Ask in the Photo section and you'll get STILLS!
As I shoot both I'll tell you what I think about each (very briefly).
Video - love it. Show the action really well. It's pretty easy to get reasonable footage and as your skills develop you can start shooting tougher shots. I have hours and hours of video. I've never watched most of it. Probably won't. Friends and family don't want to sit through long video sessions, so keep them short.
Stills - love it. Captures moments in time, personalities, beauty. I have to vehemently disagree with meekal above...you do not need a dslr to get more than fish butts. Most of the compact digitals will do a great job - you just need to work within their limitations. Friends/family love to see an image here or there - again, keep it short and select your best ones.
To get the best out of either, you're going to have to edit. I find editing video footage a little tedious after a while, but some love to do it. I don't spend much time editing my stills - I get them as close as possible in camera.
No matter what system you buy, still or video, low end or top of the line, you will need to learn what your camera will do and get in their and practice. It isn't the tool, it's the artist.
If you aren't quite sure, you might want to consider renting some gear for a few more dives or look at a compact digital that does both. This will let you explore video for relatively little cost - it's not exactly the same as shooting with a dedicated rig, but if you are unsure it's a great way to narrow your interests down. And you are likely to use your compact digital on land, too, so it won't sit on shelf when you aren't underwater.
Whichever you choose you'll have a great time!
