In the US we use flight attendant. Stewardess, hostess, etc. are out-of-date terms. A lot of the -ess forms have been dropped in favor of gender-neutral forms. server, business person, chairperson, postal carrier, police officer, even "actor" for both male and female actors, but you still hear actress a lot.

All of them are fine for a female. It used to be that stewardess was most commonly used. Now I think flight attendant is used more because there are more male attendants, and it is not gender specific. I have not heard air-hostess or flight-hostess so much. It does not mean there is anything wrong in using it, but it is not so common. To me "host" or "hostess" has more of the connotation of someone in charge of a private party or gathering. "Steward" or "stewardess" is more in line with an impersonal, professional capacity.

"Flight attendant" is the neutral expression, the other three clearly indicate that it is a woman who is serving on the flight. The older expressions which divide a profession into genders (eg. actor/actress, waiter/watress, host/hostess, steward/stewardess) are going out of fashion quickly in English, so now you will regularly hear a neutral word to accommodate both males and females... such as flight attendant. "Actor" and "waiter" are also becoming gender-neutral, and barman/barmaid is now "bar attendant" or "bar staff".

flight attendants will never be outdated! :P

Flight attendant is used for males and females.