1. looking cool/ scary - Very important and worth being uncomfortable for.
2. mobility - Important for working crowds to the fullest, playing in the que line, acting from room to room, etc.
3. ability to be heard - I'm a dialogue actor, so I do not like costumes that muffle me.
4. comfort - Because no one wants to wear a costume that stabs at them for 6 hours.
5. Ease of taking off and putting on - I never need bathroom breaks, so the costume goes on at the beginning of the night and comes off at close. Not an issue.
I really like how you posed these to your actors. Would you mind sharing their results?