I traveled there on and off for 3 years. Liberia is not a dangerous as is often made out.
Have someone you know or the hotel meet you at the airport or you're likely to get ripped off (as anywhere in that part of the world). During the day it pretty safe everywhere. There is not much between the airport and Monrovia. One of the best hotels, albeit a way outside of the city (on the airport road), is the Kendeja. Its on the beach, has a great pool and later at night there are normally a number of local girls who will enjoy a drink and stay with you if they're having a good time. Lots of girls come down for the beach at the weekend.
Perhaps unusually for a predominantly Christian country, Liberian girl's morals are somewhat looser than one might expect. Many will have several children all with different fathers. Having a white 'boyfriend' is seen as a status symbol. If you always smile first and gently flatter them, you will frequently get their phone number if you ask - and cell phones are one of the few things that work well there. Liberian men are very chauvinistic so if you treat them well, generally they'll respond in kind.
It is a country suffering abject poverty, so I always went for amateurs - the office workers, hotel staff, airline staff, bank staff etc... They're all inevitably trying to support a number of family members so a few dollars in exchange for a good time is par for the course there.
Finally take your own rubber - even though Liberia is one of the largest rubber producers in the world!