The "How did you contribute" dashboard from Pascal Neis [0] is a good place to explore some possible metrics. IMO some good predictors of mapping quality are:

- Focus on specific regions

- Both creation and deletion of map features, but more creation than deletion

- Unique and descriptive changeset comments

- Engagement in changeset comment discussions, both of your own and others' changes

[0] https://hdyc.neis-one.org/