I have my own favorites, and they will probably be apparent in the text. I also took all the underwater pictures on this site, and they therefore also belong to me. Differences Between Underwater and Land Photography 3. Camera systems 4. Digital Darkroom 1.
People have all sorts of reasons for having a hobby.
Some like tinkering with technology, some are driven to be the best, some like the opportunities for spending time with individuals of a like mind, some like sharing. Underwater photography offers all of these opportunities, and many more. I got into it because I was looking for new challenges in diving, and because I wanted to share my underwater experiences with others. Take a look at the very first underwater picture I took, on the right. It is also hideously overexposed.