What kind of housing are you using? I think that might limit what lens you use. I've never used a DSLR with a housing, I have a Nikonos underwater 35mm. My favorite lens with that is the 15mm. I have a digital Olympus 5050 with an underwater housing. With that I mainly use the macro feature because it's sharp as a tack. If you are going to be taking pics deeper than 10 feet, you'll probably want to use flash to retain all your colors. There's really not one "all around lens" for underwater photography, unless you can use a wide angle zoom that has a macro setting. Problem with that is, you can't zoom when a lens is in a housing. So you need to decide if you are going to take close up stuff or wide angle shots.