I am going through the same thing right now. I am leaning towards the Nikon becuase there are better deals on the body and two lenses (they seem to both spec out around the same, and I have shot both and like them) My only holdback is that the Nikon has a minimum ISO of 200, though the camera rates well in having low noise, my old days of shooting ISO 64 on Kodachrome still nag me a bit and I would like the ability to change exposure more on the ISO setting as oppossed to the f/stop or shutter speed depending on the situation, though the exposure compensation would help somewhat
For the lowlight/natural it is low noise even at the higher ISOs, I just have not tried it enough to see how it handles situations that are brighter and if the ISO 200 is too much. My guess is practically will not be an issue unless shooting on sand or macro where stepping down the f/stop is something you usually do anyway.
Unfortunately have not been able to use either of these underwater, just above. My friends have let me play with them a few times and have to pry them away from me because they are just so nice to shoot