Yes, if you want a natural laughing face it’s better to say something fresh.No, I recall a professional photographer employed by the MOD who said "say 'electric sex'". It was a far more reliable way of getting a large group to smile than "say cheese".
There was a very well-known brand of cheese here that used this scenario to advertise their product. What was ironic was that saying the name of the cheese made the people whose photo was being taken look surprised or puzzled.I’ve heard a variation on say cheese:
Say camembert (or gruyere or edam, etc, any cheese type will do )