That is a good question. There are so many!
I would pick one that my club was holding or if a friend was hold an event. the location was more in my neighborhood, or if the charity was dear to my heart. After that it might be distance of event and to event, cost, swag or if has become a ritual!
I belong to several clubs, and do try to attend most of their events.
As for charities, I don't do charities unless it is going to help an individual. Too many of the Executives of the BIG charities are making 7 figure salaries or high 6 figures. ( That to me is total BS )
I can do without swag if it helps an individual, and hate dust collectors. ( medals, buckles, plaques etc )