There is no safe term. Over here where I live 'deaf' is politically incorrect and 'hearing impaired' is the politically correct word. 'Hard of hearing' usually implies that you're old and therefore, have low to moderate hearing loss.

When I was in USA, 'hearing impaired' was politically incorrect (responses to an post on a HLAA mailing list where I used 'hearing impairment' made that clear). The PC word is 'hard of hearing' or 'deaf'. As far as I can use, those who belong to the 'deaf culture' (i.e. use sign language as their main means of communication) prefer to call themselves 'deaf' whereas others who use hearing aids or cochlear implants decide to call themselves 'hard of hearing' or 'hearing impaired'.

I don't really care either way which term you use. It is more how to use it - i.e. you shouldn't use any of these terms to derogate or mock hard of hearing/hearing impaired/deaf people.