American Heritage Dictionary:

at·ten·dant (ə-těn'dənt) Pronunciation Key
n.
1. One who attends or waits on another.
2. One who is present.
3. An accompanying thing or circumstance; a concomitant.

stew·ard (stōō'ərd, styōō'-) Pronunciation Key
n.
1. One who manages another's property, finances, or other affairs.
2. One who is in charge of the household affairs of a large estate, club, hotel, or resort.
3. A ship's officer who is in charge of provisions and dining arrangements.
4. An attendant on a ship or airplane.
An official who supervises or helps to manage an event.
6. A wine steward.

Objectively, which term affords the bearer more dignity?

For what it's worth:

flight attendant
n. A person who assists passengers in an aircraft.

P.S.: Whatever they are called, FAs should be treated with the same respect that we, as passengers, would expect to receive from them.