It tends to be a personal choice.
In the Deaf community, the PC terms are Deaf (which usually means using sign language as the primary communication mode) and hard of hearing (if you have some hearing or use spoken communication).
Outside the Deaf community, many people say they are hearing impaired, but that term can be offensive to Deaf people.
At Gallaudet we emphasize hearing levels rather than hearing loss, but I imagine it's the opposite in the mainstream.