Well, it all depends on what you want to do.
The major advantage of SLR/DSLR is the quality of the picture. You also have more choices of what kind of lens you want to use. However, the cost will be significantly higher. For underwater photography, the cost of the camera itself is pretty small in comparison to everything else.
The C5050, you can get Ikelite housing for around $US600 if you don't like the PT015. If you go with SLR camera, housing will be probably $US1500 and up, plus whatever ports you want to use with a specific lens.
Personally I like the C5050, while the picture quality is not as good, it is good enough for me. You also have a more compact package, option to use changable WAL lens underwater so you can shoot whatever you like every dive and does not have to commit yourself to one type of picture once you pick your lens of choice for that dive for the SLR camera.