I have been wanting to upgrade cameras for a long time and may finally be ready to do so. Currently for underwater photos I just use a Sealife DC600 point and shoot camera. On land I use an old Canon Rebel XT (350D), although I just started a new job at which I am using both a Nikon D200 and several Nikon D2Hses (I don't own any of the work cameras though and thus can't take them diving). Since I only have one lens (in addition to the pathetic kit lens) for my Rebel XT, I'm not stuck in a brand yet.
For new cameras I am looking at three mainly. The Nikon D300S, Canon 7D, and Canon Rebel T2i (550D). The lower cost of the 550D is VERY tempting to me, but the smaller size and lower build quality could be an issue (not to mention look unprofessional if I ever start freelance photography).
So I guess the main question I have for everyone here is which do you think would be best for underwater photography? Would Nikon or Canon have a better selection of lenses for underwater within reasonable prices? Does one have a better auto focus underwater or low light performance? Does the live view option on these work about the same and do any even work well underwater (I've heard it's slow)? And of course if there are any other deciding details I'm missing, please let me know!
I have a feeling this new camera will lock me into whichever brand for years to come, but both brands are just so similar in offerings currently.
Thank you everyone for your help!