It is no different in Meteor world. Your options are more or less the same:
Store on mongodb and join (if the values are likely to get updated)
Store in meteor settings and load with app
Store in a global (or namespaced) variable
Store in a variable within the method/function that assigns the ranks to the person documents
Store within the schema definition if you are using simple schema
It does not make much difference just because this is Meteor really. What matters is the application design tailored towards the specific requirements of that app.
That being said, I would go easy on joins and lookups and this is still also a valid argument with any database technology but a slightly bigger concern with mongodb.