I started out shooting video, then added film camera, alternating, then started taking both, and at one point even designed a mount so I could have my video rig atop my still camera with a quick release so I could use both on the same dive! Now I only do stills, but there are definite advantages and drawbacks to both IMO:
VIDEO
Pros:
- Easier to start out and get very good results just using a red filter
- Gives your audience much more of a "feel" for what you experienced
Cons:
- Takes dramatically more time to process/edit after you return from a trip, choosing clips, adding music, etc. - if you are retired and/or have lots of time at home after returning from a dive trip, this isn't a problem, but if you're a workaholic, you'll have a hard time ever getting your footage edited...
- Unless you have multiple audiences to which you can show it, you're likely (after all that work) to only show it a few times, an nobody will really want to see it over and over again, so it will then sit on the shelf thereafter
- Although some camcorders have still capabilities, you are unlikely to get "great" stills without strobes and a "real" still uw camera rig
STILL PHOTOGRAPHY
Pros:
- You can probably process (delete the bad and crop/edit the good in Photoshop) your work while ON a trip, or finish shortly thereafter.
- Once in awhile you'll get a great shot worthy of printing and hanging on your wall, sending prints to friends, etc., where it can be enjoyed/appreciated daily.
- Easier to send to friends, post on the internet, etc.
Cons:
- Very frustrating at first - takes awhile to get the hang of it and start getting very good results
- Doesn't convey the "feeling" of being underwater nearly as well
- Did I mention how frustrating it can be and how many crappy shots you'll get of things you thought would make great photos?!
SUMMARY
- Just starting out, and if you have plenty of spare time at home for editing, video is a great option. And if you have an outlet/audience for your videos, you may never want to do anything else!
- Whichever you do, remember to: 1. Get closer to your subjects, and 2. Get low and try to get/keep as much blue water in the viewfinder (i.e. behind and around your subjects) as possible; don't shoot down at things in the reef if you can possibly help it!
- Have fun! And welcome to the world of hobby-turned-obsession! 