When we are in meta and we click on user, we can sort them by participation. According to the description, it measures the activity.
I suggest to make something similar for the main site, for example based on the total activity (answers, comments, edits, asked questions, reviews). We could for example display that in a disk with colors associated with each kind of activity. Then the existing section "Editors" will be contained in "Activity", like the other types.
"Activity" as defined before is, to my mind, like reputation, a good way to have an idea about the contribution of an user to the site.
What do you think?