The first is simply a name for a female flight attendant, the male would be a steward. Similar to waiter/waitress, lion/lioness. A flight attendant is a member of the cabin crew. Cabin crew are responsible for the safety of passengers and serving food/drinks etc.

The first is considered insulting to women. The second is an accepted term for those providing passenger services and maintaining inflight safety. The third is a more generic term for those looking after passengers.