In addition to choosing based on the type of camera you have, you should consider the following characteristics when shopping for a new housing: depth rating, material, ease of use, the type of connection to your strobes, port options, and available accessories.
Underwater housings are primarily manufactured either out of polycarbonate or aluminum, rarely of both together. Plastic housings are more affordable but somewhat bulkier and less durable in the long run. Aluminum housings are much more rugged and finely machined. These, however, can come with a hefty price tag. Due to the fact that you have to choose a housing for a specific camera model, you may be limited in options. For example, most compact cameras come only with plastic housing options.
As for the depth rating, you should always choose a housing with a rating that exceeds the depth you plan to dive. Going beyond the housing’s recommended depth rating may cause it to leak or even implode.
Make sure to check whether the housing provides access to all the camera functions you want. Also, look if you can conveniently connect your strobes to the housing. The idea is to find the housing that will allow you to concentrate on your perfect shot, rather than equipment.