There's no right answer, but it's helpful to think about it from a data modeling point of view. If where the update comes from would be stored as an attribute

There's no right answer, but it's helpful to think about it from a data modeling point of view. If where the update comes from would be stored as an attribute (i.e. column in the table), use the parameter option (/update?from=GitHub). If, however, they'd be separate types of updates (i.e. separate tables), use the separate URIs (/update/github or /github_update). This is an analogy, of course, as there's no need for a 1-to-1 resource-persistance mapping, but it's a useful way of thinking about it, I think.