Who should receive pre-exposure HIV prophylaxis?

No one? If you dont have any exposure, you dont need routine testing / prophylaxis. If you feel that you may have exposure via unprotected intercouse with an infected partner, or sharing needles with someone who may be infected, then you may need to speak to a physician for testing and prophylactic treatment.
Why, why, why? You shouldn't even consider having sex with someone infected with hiv. There is no silver bullet other than avoidance. Your question is like asking what are my chances of getting killed when playing russian roulette. Why?